diff --git a/Makefile b/Makefile
index 04c36d4..92280cd 100644
--- a/Makefile
+++ b/Makefile
@@ -3,7 +3,7 @@
 all: clean-pyc test
 
 test:
-	@cd tests; python tests.py
+	@pytest
 
 tox-test:
 	@tox
diff --git a/flask_babel/__init__.py b/flask_babel/__init__.py
index 2664676..7a479fa 100644
--- a/flask_babel/__init__.py
+++ b/flask_babel/__init__.py
@@ -15,6 +15,7 @@
 from contextlib import contextmanager
 from flask import current_app, request
 from flask.ctx import has_request_context
+from flask.helpers import locked_cached_property
 from babel import dates, numbers, support, Locale
 from pytz import timezone, UTC
 from werkzeug.datastructures import ImmutableDict
@@ -185,6 +186,12 @@ def domain(self):
         """
         return self.app.config['BABEL_DOMAIN']
 
+    @locked_cached_property
+    def domain_instance(self):
+        """The message domain for the translations.
+        """
+        return Domain(domain=self.app.config['BABEL_DOMAIN'])
+
     @property
     def translation_directories(self):
         directories = self.app.config.get(
@@ -205,33 +212,7 @@ def get_translations():
     object if used outside of the request or if a translation cannot be
     found.
     """
-    ctx = _get_current_context()
-
-    if ctx is None:
-        return support.NullTranslations()
-
-    translations = getattr(ctx, 'babel_translations', None)
-    if translations is None:
-        translations = support.Translations()
-
-        babel = current_app.extensions['babel']
-        for dirname in babel.translation_directories:
-            catalog = support.Translations.load(
-                    dirname,
-                    [get_locale()],
-                    babel.domain
-                )
-            translations.merge(catalog)
-            # FIXME: Workaround for merge() being really, really stupid. It
-            # does not copy _info, plural(), or any other instance variables
-            # populated by GNUTranslations. We probably want to stop using
-            # `support.Translations.merge` entirely.
-            if hasattr(catalog, 'plural'):
-                translations.plural = catalog.plural
-
-        ctx.babel_translations = translations
-
-    return translations
+    return get_domain().get_translations()
 
 
 def get_locale():
@@ -472,7 +453,7 @@ def format_number(number):
     :rtype: unicode
     """
     locale = get_locale()
-    return numbers.format_number(number, locale=locale)
+    return numbers.format_decimal(number, locale=locale)
 
 
 def format_decimal(number, format=None):
@@ -536,108 +517,167 @@ def format_scientific(number, format=None):
     return numbers.format_scientific(number, format=format, locale=locale)
 
 
-def gettext(string, **variables):
-    """Translates a string with the current locale and passes in the
-    given keyword arguments as mapping to a string formatting string.
+class Domain(object):
+    """Localization domain. By default will use look for tranlations in Flask
+    application directory and "messages" domain - all message catalogs should
+    be called ``messages.mo``.
+    """
+
+    def __init__(self, translation_directories=None, domain='messages'):
+        if isinstance(translation_directories, string_types):
+            translation_directories = [translation_directories]
+        self._translation_directories = translation_directories
+        self.domain = domain
+        self.cache = {}
 
-    ::
+    def __repr__(self):
+        return '<Domain({!r}, {!r})>'.format(self._translation_directories, self.domain)
 
-        gettext(u'Hello World!')
-        gettext(u'Hello %(name)s!', name='World')
-    """
-    t = get_translations()
-    if t is None:
-        return string if not variables else string % variables
-    s = t.ugettext(string)
-    return s if not variables else s % variables
-_ = gettext
+    @property
+    def translation_directories(self):
+        if self._translation_directories is not None:
+            return self._translation_directories
+        babel = current_app.extensions['babel']
+        return babel.translation_directories
 
+    def as_default(self):
+        """Set this domain as default for the current request"""
+        ctx = _get_current_context()
 
-def ngettext(singular, plural, num, **variables):
-    """Translates a string with the current locale and passes in the
-    given keyword arguments as mapping to a string formatting string.
-    The `num` parameter is used to dispatch between singular and various
-    plural forms of the message.  It is available in the format string
-    as ``%(num)d`` or ``%(num)s``.  The source language should be
-    English or a similar language which only has one plural form.
+        if ctx is None:
+            raise RuntimeError("No request context")
 
-    ::
+        ctx.babel_domain = self
 
-        ngettext(u'%(num)d Apple', u'%(num)d Apples', num=len(apples))
-    """
-    variables.setdefault('num', num)
-    t = get_translations()
-    if t is None:
-        s = singular if num == 1 else plural
-        return s if not variables else s % variables
+    def get_translations_cache(self, ctx):
+        """Returns dictionary-like object for translation caching"""
+        return self.cache
 
-    s = t.ungettext(singular, plural, num)
-    return s if not variables else s % variables
+    def get_translations(self):
+        ctx = _get_current_context()
 
+        if ctx is None:
+            return support.NullTranslations()
 
-def pgettext(context, string, **variables):
-    """Like :func:`gettext` but with a context.
+        cache = self.get_translations_cache(ctx)
+        locale = get_locale()
+        try:
+            return cache[str(locale), self.domain]
+        except KeyError:
+            translations = support.Translations()
 
-    .. versionadded:: 0.7
-    """
-    t = get_translations()
-    if t is None:
-        return string if not variables else string % variables
-    s = t.upgettext(context, string)
-    return s if not variables else s % variables
+            for dirname in self.translation_directories:
+                catalog = support.Translations.load(
+                    dirname,
+                    [locale],
+                    self.domain
+                )
+                translations.merge(catalog)
+                # FIXME: Workaround for merge() being really, really stupid. It
+                # does not copy _info, plural(), or any other instance variables
+                # populated by GNUTranslations. We probably want to stop using
+                # `support.Translations.merge` entirely.
+                if hasattr(catalog, 'plural'):
+                    translations.plural = catalog.plural
 
+            cache[str(locale), self.domain] = translations
+            return translations
 
-def npgettext(context, singular, plural, num, **variables):
-    """Like :func:`ngettext` but with a context.
+    def gettext(self, string, **variables):
+        """Translates a string with the current locale and passes in the
+        given keyword arguments as mapping to a string formatting string.
 
-    .. versionadded:: 0.7
-    """
-    variables.setdefault('num', num)
-    t = get_translations()
-    if t is None:
-        s = singular if num == 1 else plural
+        ::
+
+            gettext(u'Hello World!')
+            gettext(u'Hello %(name)s!', name='World')
+        """
+        t = self.get_translations()
+        if t is None:
+            return string if not variables else string % variables
+        s = t.ugettext(string)
         return s if not variables else s % variables
-    s = t.unpgettext(context, singular, plural, num)
-    return s if not variables else s % variables
 
+    def ngettext(self, singular, plural, num, **variables):
+        """Translates a string with the current locale and passes in the
+        given keyword arguments as mapping to a string formatting string.
+        The `num` parameter is used to dispatch between singular and various
+        plural forms of the message.  It is available in the format string
+        as ``%(num)d`` or ``%(num)s``.  The source language should be
+        English or a similar language which only has one plural form.
 
-def lazy_gettext(string, **variables):
-    """Like :func:`gettext` but the string returned is lazy which means
-    it will be translated when it is used as an actual string.
+        ::
 
-    Example::
+            ngettext(u'%(num)d Apple', u'%(num)d Apples', num=len(apples))
+        """
+        variables.setdefault('num', num)
+        t = self.get_translations()
+        if t is None:
+            s = singular if num == 1 else plural
+            return s if not variables else s % variables
 
-        hello = lazy_gettext(u'Hello World')
+        s = t.ungettext(singular, plural, num)
+        return s if not variables else s % variables
 
-        @app.route('/')
-        def index():
-            return unicode(hello)
-    """
-    return LazyString(gettext, string, **variables)
+    def pgettext(self, context, string, **variables):
+        """Like :func:`gettext` but with a context.
 
+        .. versionadded:: 0.7
+        """
+        t = self.get_translations()
+        if t is None:
+            return string if not variables else string % variables
+        s = t.upgettext(context, string)
+        return s if not variables else s % variables
 
-def lazy_ngettext(singular, plural, num, **variables):
-    """Like :func:`ngettext` but the string returned is lazy which means
-    it will be translated when it is used as an actual string.
+    def npgettext(self, context, singular, plural, num, **variables):
+        """Like :func:`ngettext` but with a context.
 
-    Example::
+        .. versionadded:: 0.7
+        """
+        variables.setdefault('num', num)
+        t = self.get_translations()
+        if t is None:
+            s = singular if num == 1 else plural
+            return s if not variables else s % variables
+        s = t.unpgettext(context, singular, plural, num)
+        return s if not variables else s % variables
 
-        apples = lazy_ngettext(u'%(num)d Apple', u'%(num)d Apples', num=len(apples))
+    def lazy_gettext(self, string, **variables):
+        """Like :func:`gettext` but the string returned is lazy which means
+        it will be translated when it is used as an actual string.
 
-        @app.route('/')
-        def index():
-            return unicode(apples)
-    """
-    return LazyString(ngettext, singular, plural, num, **variables)
+        Example::
 
+            hello = lazy_gettext(u'Hello World')
 
-def lazy_pgettext(context, string, **variables):
-    """Like :func:`pgettext` but the string returned is lazy which means
-    it will be translated when it is used as an actual string.
+            @app.route('/')
+            def index():
+                return unicode(hello)
+        """
+        return LazyString(self.gettext, string, **variables)
 
-    .. versionadded:: 0.7
-    """
-    return LazyString(pgettext, context, string, **variables)
+    def lazy_ngettext(self, singular, plural, num, **variables):
+        """Like :func:`ngettext` but the string returned is lazy which means
+        it will be translated when it is used as an actual string.
+
+        Example::
+
+            apples = lazy_ngettext(u'%(num)d Apple', u'%(num)d Apples', num=len(apples))
+
+            @app.route('/')
+            def index():
+                return unicode(apples)
+        """
+        return LazyString(self.ngettext, singular, plural, num, **variables)
+
+    def lazy_pgettext(self, context, string, **variables):
+        """Like :func:`pgettext` but the string returned is lazy which means
+        it will be translated when it is used as an actual string.
+
+        .. versionadded:: 0.7
+        """
+        return LazyString(self.pgettext, context, string, **variables)
 
 
 def _get_current_context():
@@ -646,3 +686,49 @@ def _get_current_context():
 
     if current_app:
         return current_app
+
+
+def get_domain():
+    ctx = _get_current_context()
+    if ctx is None:
+        # this will use NullTranslations
+        return Domain()
+
+    try:
+        return ctx.babel_domain
+    except AttributeError:
+        pass
+
+    babel = current_app.extensions['babel']
+    ctx.babel_domain = babel.domain_instance
+    return ctx.babel_domain
+
+
+# Create shortcuts for the default Flask domain
+def gettext(*args, **kwargs):
+    return get_domain().gettext(*args, **kwargs)
+_ = gettext
+
+
+def ngettext(*args, **kwargs):
+    return get_domain().ngettext(*args, **kwargs)
+
+
+def pgettext(*args, **kwargs):
+    return get_domain().pgettext(*args, **kwargs)
+
+
+def npgettext(*args, **kwargs):
+    return get_domain().npgettext(*args, **kwargs)
+
+
+def lazy_gettext(*args, **kwargs):
+    return LazyString(gettext, *args, **kwargs)
+
+
+def lazy_pgettext(*args, **kwargs):
+    return LazyString(pgettext, *args, **kwargs)
+
+
+def lazy_ngettext(*args, **kwargs):
+    return LazyString(ngettext, *args, **kwargs)
diff --git a/flask_babel/speaklater.py b/flask_babel/speaklater.py
index 489f73b..206ed84 100644
--- a/flask_babel/speaklater.py
+++ b/flask_babel/speaklater.py
@@ -74,4 +74,4 @@ def __mod__(self, other):
         return text_type(self) % other
 
     def __rmod__(self, other):
-        return other + text_type(self)
\ No newline at end of file
+        return other + text_type(self)
diff --git a/pytest.ini b/pytest.ini
new file mode 100644
index 0000000..29e9bf1
--- /dev/null
+++ b/pytest.ini
@@ -0,0 +1,3 @@
+[pytest]
+addopts =
+    tests/
diff --git a/setup.py b/setup.py
index f696bf1..0133fb9 100644
--- a/setup.py
+++ b/setup.py
@@ -37,5 +37,11 @@
         'Programming Language :: Python :: Implementation :: PyPy',
         'Topic :: Internet :: WWW/HTTP :: Dynamic Content',
         'Topic :: Software Development :: Libraries :: Python Modules'
-    ]
+    ],
+    extras_require={
+        'dev': [
+            'pytest',
+            'pytest-mock'
+        ]
+    }
 )
diff --git a/tests/renamed_translations/de/LC_MESSAGES/myapp.mo b/tests/renamed_translations/de/LC_MESSAGES/myapp.mo
new file mode 100644
index 0000000..041aa3c
Binary files /dev/null and b/tests/renamed_translations/de/LC_MESSAGES/myapp.mo differ
diff --git a/tests/renamed_translations/de/LC_MESSAGES/myapp.po b/tests/renamed_translations/de/LC_MESSAGES/myapp.po
new file mode 100644
index 0000000..6d6ea80
--- /dev/null
+++ b/tests/renamed_translations/de/LC_MESSAGES/myapp.po
@@ -0,0 +1,35 @@
+# German translations for PROJECT.
+# Copyright (C) 2010 ORGANIZATION
+# This file is distributed under the same license as the PROJECT project.
+# FIRST AUTHOR <EMAIL@ADDRESS>, 2010.
+#
+msgid ""
+msgstr ""
+"Project-Id-Version: PROJECT VERSION\n"
+"Report-Msgid-Bugs-To: EMAIL@ADDRESS\n"
+"POT-Creation-Date: 2010-05-29 17:00+0200\n"
+"PO-Revision-Date: 2010-05-30 12:56+0200\n"
+"Last-Translator: Armin Ronacher <armin.ronacher@active-4.com>\n"
+"Language-Team: de <LL@li.org>\n"
+"Plural-Forms: nplurals=2; plural=(n != 1)\n"
+"MIME-Version: 1.0\n"
+"Content-Type: text/plain; charset=utf-8\n"
+"Content-Transfer-Encoding: 8bit\n"
+"Generated-By: Babel 0.9.5\n"
+
+#: tests.py:94
+#, python-format
+msgid "Hello %(name)s!"
+msgstr "Hallo %(name)s!"
+
+#: tests.py:95 tests.py:96
+#, python-format
+msgid "%(num)s Apple"
+msgid_plural "%(num)s Apples"
+msgstr[0] "%(num)s Apfel"
+msgstr[1] "%(num)s Äpfel"
+
+#: tests.py:119
+msgid "Yes"
+msgstr "Ja"
+
diff --git a/tests/test_date_formatting.py b/tests/test_date_formatting.py
new file mode 100644
index 0000000..83f1736
--- /dev/null
+++ b/tests/test_date_formatting.py
@@ -0,0 +1,166 @@
+# -*- coding: utf-8 -*-
+from __future__ import with_statement
+
+from datetime import datetime, timedelta
+from threading import Semaphore, Thread
+
+import flask
+
+import flask_babel as babel
+
+
+def test_basics():
+    app = flask.Flask(__name__)
+    babel.Babel(app)
+    d = datetime(2010, 4, 12, 13, 46)
+    delta = timedelta(days=6)
+
+    with app.test_request_context():
+        assert babel.format_datetime(d) == 'Apr 12, 2010, 1:46:00 PM'
+        assert babel.format_date(d) == 'Apr 12, 2010'
+        assert babel.format_time(d) == '1:46:00 PM'
+        assert babel.format_timedelta(delta) == '1 week'
+        assert babel.format_timedelta(delta, threshold=1) == '6 days'
+
+    with app.test_request_context():
+        app.config['BABEL_DEFAULT_TIMEZONE'] = 'Europe/Vienna'
+        assert babel.format_datetime(d) == 'Apr 12, 2010, 3:46:00 PM'
+        assert babel.format_date(d) == 'Apr 12, 2010'
+        assert babel.format_time(d) == '3:46:00 PM'
+
+    with app.test_request_context():
+        app.config['BABEL_DEFAULT_LOCALE'] = 'de_DE'
+        assert babel.format_datetime(d, 'long') == \
+            '12. April 2010 um 15:46:00 MESZ'
+
+
+def test_init_app():
+    b = babel.Babel()
+    app = flask.Flask(__name__)
+    b.init_app(app)
+    d = datetime(2010, 4, 12, 13, 46)
+
+    with app.test_request_context():
+        assert babel.format_datetime(d) == 'Apr 12, 2010, 1:46:00 PM'
+        assert babel.format_date(d) == 'Apr 12, 2010'
+        assert babel.format_time(d) == '1:46:00 PM'
+
+    with app.test_request_context():
+        app.config['BABEL_DEFAULT_TIMEZONE'] = 'Europe/Vienna'
+        assert babel.format_datetime(d) == 'Apr 12, 2010, 3:46:00 PM'
+        assert babel.format_date(d) == 'Apr 12, 2010'
+        assert babel.format_time(d) == '3:46:00 PM'
+
+    with app.test_request_context():
+        app.config['BABEL_DEFAULT_LOCALE'] = 'de_DE'
+        assert babel.format_datetime(d, 'long') == \
+            '12. April 2010 um 15:46:00 MESZ'
+
+
+def test_custom_formats():
+    app = flask.Flask(__name__)
+    app.config.update(
+        BABEL_DEFAULT_LOCALE='en_US',
+        BABEL_DEFAULT_TIMEZONE='Pacific/Johnston'
+    )
+    b = babel.Babel(app)
+    b.date_formats['datetime'] = 'long'
+    b.date_formats['datetime.long'] = 'MMMM d, yyyy h:mm:ss a'
+    d = datetime(2010, 4, 12, 13, 46)
+
+    with app.test_request_context():
+        assert babel.format_datetime(d) == 'April 12, 2010 3:46:00 AM'
+
+
+def test_custom_locale_selector():
+    app = flask.Flask(__name__)
+    b = babel.Babel(app)
+    d = datetime(2010, 4, 12, 13, 46)
+
+    the_timezone = 'UTC'
+    the_locale = 'en_US'
+
+    @b.localeselector
+    def select_locale():
+        return the_locale
+
+    @b.timezoneselector
+    def select_timezone():
+        return the_timezone
+
+    with app.test_request_context():
+        assert babel.format_datetime(d) == 'Apr 12, 2010, 1:46:00 PM'
+
+    the_locale = 'de_DE'
+    the_timezone = 'Europe/Vienna'
+
+    with app.test_request_context():
+        assert babel.format_datetime(d) == '12.04.2010, 15:46:00'
+
+
+def test_refreshing():
+    app = flask.Flask(__name__)
+    babel.Babel(app)
+    d = datetime(2010, 4, 12, 13, 46)
+    with app.test_request_context():
+        assert babel.format_datetime(d) == 'Apr 12, 2010, 1:46:00 PM'
+        app.config['BABEL_DEFAULT_TIMEZONE'] = 'Europe/Vienna'
+        babel.refresh()
+        assert babel.format_datetime(d) == 'Apr 12, 2010, 3:46:00 PM'
+
+
+def test_force_locale():
+    app = flask.Flask(__name__)
+    b = babel.Babel(app)
+
+    @b.localeselector
+    def select_locale():
+        return 'de_DE'
+
+    with app.test_request_context():
+        assert str(babel.get_locale()) == 'de_DE'
+        with babel.force_locale('en_US'):
+            assert str(babel.get_locale()) == 'en_US'
+        assert str(babel.get_locale()) == 'de_DE'
+
+
+def test_force_locale_with_threading():
+    app = flask.Flask(__name__)
+    b = babel.Babel(app)
+
+    @b.localeselector
+    def select_locale():
+        return 'de_DE'
+
+    semaphore = Semaphore(value=0)
+
+    def first_request():
+        with app.test_request_context():
+            with babel.force_locale('en_US'):
+                assert str(babel.get_locale()) == 'en_US'
+                semaphore.acquire()
+
+    thread = Thread(target=first_request)
+    thread.start()
+
+    try:
+        with app.test_request_context():
+            assert str(babel.get_locale()) == 'de_DE'
+    finally:
+        semaphore.release()
+        thread.join()
+
+
+def test_refresh_during_force_locale():
+    app = flask.Flask(__name__)
+    b = babel.Babel(app)
+
+    @b.localeselector
+    def select_locale():
+        return 'de_DE'
+
+    with app.test_request_context():
+        with babel.force_locale('en_US'):
+            assert str(babel.get_locale()) == 'en_US'
+            babel.refresh()
+            assert str(babel.get_locale()) == 'en_US'
diff --git a/tests/test_gettext.py b/tests/test_gettext.py
new file mode 100644
index 0000000..b8b65a3
--- /dev/null
+++ b/tests/test_gettext.py
@@ -0,0 +1,201 @@
+# -*- coding: utf-8 -*-
+from __future__ import with_statement
+
+import flask
+
+import flask_babel as babel
+from flask_babel import gettext, lazy_gettext, lazy_ngettext, ngettext
+from flask_babel._compat import text_type
+
+
+def test_basics():
+    app = flask.Flask(__name__)
+    babel.Babel(app, default_locale='de_DE')
+
+    with app.test_request_context():
+        assert gettext(u'Hello %(name)s!', name='Peter') == 'Hallo Peter!'
+        assert ngettext(u'%(num)s Apple', u'%(num)s Apples', 3) == \
+            u'3 Äpfel'
+        assert ngettext(u'%(num)s Apple', u'%(num)s Apples', 1) == \
+            u'1 Apfel'
+
+
+def test_template_basics():
+    app = flask.Flask(__name__)
+    babel.Babel(app, default_locale='de_DE')
+
+    t = lambda x: flask.render_template_string('{{ %s }}' % x)
+
+    with app.test_request_context():
+        assert t("gettext('Hello %(name)s!', name='Peter')") == \
+            u'Hallo Peter!'
+        assert t("ngettext('%(num)s Apple', '%(num)s Apples', 3)") == \
+            u'3 Äpfel'
+        assert t("ngettext('%(num)s Apple', '%(num)s Apples', 1)") == \
+            u'1 Apfel'
+        assert flask.render_template_string('''
+            {% trans %}Hello {{ name }}!{% endtrans %}
+        ''', name='Peter').strip() == 'Hallo Peter!'
+        assert flask.render_template_string('''
+            {% trans num=3 %}{{ num }} Apple
+            {%- pluralize %}{{ num }} Apples{% endtrans %}
+        ''', name='Peter').strip() == u'3 Äpfel'
+
+
+def test_lazy_gettext():
+    app = flask.Flask(__name__)
+    babel.Babel(app, default_locale='de_DE')
+    yes = lazy_gettext(u'Yes')
+    with app.test_request_context():
+        assert text_type(yes) == 'Ja'
+        assert yes.__html__() == 'Ja'
+    app.config['BABEL_DEFAULT_LOCALE'] = 'en_US'
+    with app.test_request_context():
+        assert text_type(yes) == 'Yes'
+        assert yes.__html__() == 'Yes'
+
+
+def test_lazy_ngettext():
+    app = flask.Flask(__name__)
+    babel.Babel(app, default_locale='de_DE')
+    one_apple = lazy_ngettext(u'%(num)s Apple', u'%(num)s Apples', 1)
+    with app.test_request_context():
+        assert text_type(one_apple) == '1 Apfel'
+        assert one_apple.__html__() == '1 Apfel'
+    two_apples = lazy_ngettext(u'%(num)s Apple', u'%(num)s Apples', 2)
+    with app.test_request_context():
+        assert text_type(two_apples) == u'2 Äpfel'
+        assert two_apples.__html__() == u'2 Äpfel'
+
+
+def test_lazy_gettext_defaultdomain():
+    app = flask.Flask(__name__)
+    b = babel.Babel(app, default_locale='de_DE', default_domain='test')
+    first = lazy_gettext('first')
+    with app.test_request_context():
+        assert text_type(first) == 'erste'
+    app.config['BABEL_DEFAULT_LOCALE'] = 'en_US'
+    with app.test_request_context():
+        assert text_type(first) == 'first'
+
+
+def test_list_translations():
+    app = flask.Flask(__name__)
+    b = babel.Babel(app, default_locale='de_DE')
+    translations = b.list_translations()
+    assert len(translations) == 1
+    assert str(translations[0]) == 'de'
+
+
+def test_no_formatting():
+    """
+    Ensure we don't format strings unless a variable is passed.
+    """
+    app = flask.Flask(__name__)
+    babel.Babel(app)
+
+    with app.test_request_context():
+        assert gettext(u'Test %s') == u'Test %s'
+        assert gettext(u'Test %(name)s', name=u'test') == u'Test test'
+        assert gettext(u'Test %s') % 'test' == u'Test test'
+
+
+def test_domain():
+    app = flask.Flask(__name__)
+    b = babel.Babel(app, default_locale='de_DE')
+    domain = babel.Domain(domain='test')
+
+    with app.test_request_context():
+        assert domain.gettext('first') == 'erste'
+        assert babel.gettext('first') == 'first'
+
+
+def test_as_default():
+    app = flask.Flask(__name__)
+    b = babel.Babel(app, default_locale='de_DE')
+    domain = babel.Domain(domain='test')
+
+    with app.test_request_context():
+        assert babel.gettext('first') == 'first'
+        domain.as_default()
+        assert babel.gettext('first') == 'erste'
+
+
+def test_default_domain():
+    app = flask.Flask(__name__)
+    b = babel.Babel(app, default_locale='de_DE', default_domain='test')
+
+    with app.test_request_context():
+        assert babel.gettext('first') == 'erste'
+
+
+def test_multiple_apps():
+    app1 = flask.Flask(__name__)
+    b1 = babel.Babel(app1, default_locale='de_DE')
+
+    app2 = flask.Flask(__name__)
+    b2 = babel.Babel(app2, default_locale='de_DE')
+
+    with app1.test_request_context() as ctx:
+        assert babel.gettext('Yes') == 'Ja'
+
+        assert ('de_DE', 'messages') in b1.domain_instance.get_translations_cache(ctx)
+
+    with app2.test_request_context() as ctx:
+        assert 'de_DE', 'messages' not in b2.domain_instance.get_translations_cache(ctx)
+
+
+def test_cache(mocker):
+    load_mock = mocker.patch(
+        "babel.support.Translations.load", side_effect=babel.support.Translations.load
+    )
+
+    app = flask.Flask(__name__)
+    b = babel.Babel(app, default_locale="de_DE")
+
+    @b.localeselector
+    def select_locale():
+        return the_locale
+
+    # first request, should load en_US
+    the_locale = "en_US"
+    with app.test_request_context() as ctx:
+        assert b.domain_instance.get_translations_cache(ctx) == {}
+        assert babel.gettext("Yes") == "Yes"
+    assert load_mock.call_count == 1
+
+    # second request, should use en_US from cache
+    with app.test_request_context() as ctx:
+        assert set(b.domain_instance.get_translations_cache(ctx)) == {
+            ("en_US", "messages")
+        }
+        assert babel.gettext("Yes") == "Yes"
+    assert load_mock.call_count == 1
+
+    # third request, should load de_DE from cache
+    the_locale = "de_DE"
+    with app.test_request_context() as ctx:
+        assert set(b.domain_instance.get_translations_cache(ctx)) == {
+            ("en_US", "messages")
+        }
+        assert babel.gettext("Yes") == "Ja"
+    assert load_mock.call_count == 2
+
+    # now everything is cached, so no more loads should happen!
+    the_locale = "en_US"
+    with app.test_request_context() as ctx:
+        assert set(b.domain_instance.get_translations_cache(ctx)) == {
+            ("en_US", "messages"),
+            ("de_DE", "messages"),
+        }
+        assert babel.gettext("Yes") == "Yes"
+    assert load_mock.call_count == 2
+
+    the_locale = "de_DE"
+    with app.test_request_context() as ctx:
+        assert set(b.domain_instance.get_translations_cache(ctx)) == {
+            ("en_US", "messages"),
+            ("de_DE", "messages"),
+        }
+        assert babel.gettext("Yes") == "Ja"
+    assert load_mock.call_count == 2
diff --git a/tests/test_integration.py b/tests/test_integration.py
new file mode 100644
index 0000000..2cd6f6c
--- /dev/null
+++ b/tests/test_integration.py
@@ -0,0 +1,122 @@
+# -*- coding: utf-8 -*-
+from __future__ import with_statement
+
+import pickle
+
+import flask
+from babel.support import NullTranslations
+
+import flask_babel as babel
+from flask_babel import get_translations, gettext, lazy_gettext
+
+
+def test_no_request_context():
+    b = babel.Babel()
+    app = flask.Flask(__name__)
+    b.init_app(app)
+
+    with app.app_context():
+        assert isinstance(get_translations(), NullTranslations)
+
+
+def test_multiple_directories():
+    """
+    Ensure we can load translations from multiple directories.
+    """
+    b = babel.Babel()
+    app = flask.Flask(__name__)
+
+    app.config.update({
+        'BABEL_TRANSLATION_DIRECTORIES': ';'.join((
+            'translations',
+            'renamed_translations'
+        )),
+        'BABEL_DEFAULT_LOCALE': 'de_DE'
+    })
+
+    b.init_app(app)
+
+    with app.test_request_context():
+        translations = b.list_translations()
+
+        assert(len(translations) == 2)
+        assert(str(translations[0]) == 'de')
+        assert(str(translations[1]) == 'de')
+
+        assert gettext(
+            u'Hello %(name)s!',
+            name='Peter'
+        ) == 'Hallo Peter!'
+
+
+def test_multiple_directories_different_domain():
+    """
+    Ensure we can load translations from multiple directories with a
+    custom domain.
+    """
+    b = babel.Babel()
+    app = flask.Flask(__name__)
+
+    app.config.update({
+        'BABEL_TRANSLATION_DIRECTORIES': ';'.join((
+            'translations_different_domain',
+            'renamed_translations'
+        )),
+        'BABEL_DEFAULT_LOCALE': 'de_DE',
+        'BABEL_DOMAIN': 'myapp'
+    })
+
+    b.init_app(app)
+
+    with app.test_request_context():
+        translations = b.list_translations()
+
+        assert(len(translations) == 2)
+        assert(str(translations[0]) == 'de')
+        assert(str(translations[1]) == 'de')
+
+        assert gettext(
+            u'Hello %(name)s!',
+            name='Peter'
+        ) == 'Hallo Peter!'
+        assert gettext(u'Good bye') == 'Auf Wiedersehen'
+
+
+def test_different_domain():
+    """
+    Ensure we can load translations from multiple directories.
+    """
+    b = babel.Babel()
+    app = flask.Flask(__name__)
+
+    app.config.update({
+        'BABEL_TRANSLATION_DIRECTORIES': 'translations_different_domain',
+        'BABEL_DEFAULT_LOCALE': 'de_DE',
+        'BABEL_DOMAIN': 'myapp'
+    })
+
+    b.init_app(app)
+
+    with app.test_request_context():
+        translations = b.list_translations()
+
+        assert(len(translations) == 1)
+        assert(str(translations[0]) == 'de')
+
+        assert gettext(u'Good bye') == 'Auf Wiedersehen'
+
+
+def test_lazy_old_style_formatting():
+    lazy_string = lazy_gettext(u'Hello %(name)s')
+    assert lazy_string % {u'name': u'test'} == u'Hello test'
+
+    lazy_string = lazy_gettext(u'test')
+    assert u'Hello %s' % lazy_string == u'Hello test'
+
+
+def test_lazy_pickling():
+    lazy_string = lazy_gettext(u'Foo')
+    pickled = pickle.dumps(lazy_string)
+    unpickled = pickle.loads(pickled)
+
+    assert unpickled == lazy_string
diff --git a/tests/test_number_formatting.py b/tests/test_number_formatting.py
new file mode 100644
index 0000000..bd59617
--- /dev/null
+++ b/tests/test_number_formatting.py
@@ -0,0 +1,21 @@
+# -*- coding: utf-8 -*-
+from __future__ import with_statement
+
+from decimal import Decimal
+
+import flask
+
+import flask_babel as babel
+
+
+def test_basics():
+    app = flask.Flask(__name__)
+    babel.Babel(app)
+    n = 1099
+
+    with app.test_request_context():
+        assert babel.format_number(n) == u'1,099'
+        assert babel.format_decimal(Decimal('1010.99')) == u'1,010.99'
+        assert babel.format_currency(n, 'USD') == '$1,099.00'
+        assert babel.format_percent(0.19) == '19%'
+        assert babel.format_scientific(10000) == u'1E4'
diff --git a/tests/tests.py b/tests/tests.py
deleted file mode 100644
index aefba35..0000000
--- a/tests/tests.py
+++ /dev/null
@@ -1,343 +0,0 @@
-# -*- coding: utf-8 -*-
-from __future__ import with_statement
-
-import sys
-import os
-sys.path.insert(0, os.path.join(os.path.dirname(__file__), '..'))
-
-import pickle
-from threading import Thread, Semaphore
-
-import unittest
-from decimal import Decimal
-import flask
-from datetime import datetime, timedelta
-import flask_babel as babel
-from flask_babel import gettext, ngettext, lazy_gettext, lazy_ngettext, get_translations
-from babel.support import NullTranslations
-from flask_babel._compat import text_type
-
-
-class IntegrationTestCase(unittest.TestCase):
-    def test_no_request_context(self):
-        b = babel.Babel()
-        app = flask.Flask(__name__)
-        b.init_app(app)
-
-        with app.app_context():
-            assert isinstance(get_translations(), NullTranslations)
-
-    def test_multiple_directories(self):
-        """
-        Ensure we can load translations from multiple directories.
-        """
-        b = babel.Babel()
-        app = flask.Flask(__name__)
-
-        app.config.update({
-            'BABEL_TRANSLATION_DIRECTORIES': ';'.join((
-                'translations',
-                'renamed_translations'
-            )),
-            'BABEL_DEFAULT_LOCALE': 'de_DE'
-        })
-
-        b.init_app(app)
-
-        with app.test_request_context():
-            translations = b.list_translations()
-
-            assert(len(translations) == 2)
-            assert(str(translations[0]) == 'de')
-            assert(str(translations[1]) == 'de')
-
-            assert gettext(
-                u'Hello %(name)s!',
-                name='Peter'
-            ) == 'Hallo Peter!'
-
-    def test_different_domain(self):
-        """
-        Ensure we can load translations from multiple directories.
-        """
-        b = babel.Babel()
-        app = flask.Flask(__name__)
-
-        app.config.update({
-            'BABEL_TRANSLATION_DIRECTORIES': 'translations_different_domain',
-            'BABEL_DEFAULT_LOCALE': 'de_DE',
-            'BABEL_DOMAIN': 'myapp'
-        })
-
-        b.init_app(app)
-
-        with app.test_request_context():
-            translations = b.list_translations()
-
-            assert(len(translations) == 1)
-            assert(str(translations[0]) == 'de')
-
-            assert gettext(u'Good bye') == 'Auf Wiedersehen'
-
-    def test_lazy_old_style_formatting(self):
-        lazy_string = lazy_gettext(u'Hello %(name)s')
-        assert lazy_string % {u'name': u'test'} == u'Hello test'
-
-        lazy_string = lazy_gettext(u'test')
-        assert u'Hello %s' % lazy_string == u'Hello test'
-
-    def test_lazy_pickling(self):
-        lazy_string = lazy_gettext(u'Foo')
-        pickled = pickle.dumps(lazy_string)
-        unpickled = pickle.loads(pickled)
-
-        assert unpickled == lazy_string
-
-
-class DateFormattingTestCase(unittest.TestCase):
-
-    def test_basics(self):
-        app = flask.Flask(__name__)
-        babel.Babel(app)
-        d = datetime(2010, 4, 12, 13, 46)
-        delta = timedelta(days=6)
-
-        with app.test_request_context():
-            assert babel.format_datetime(d) == 'Apr 12, 2010, 1:46:00 PM'
-            assert babel.format_date(d) == 'Apr 12, 2010'
-            assert babel.format_time(d) == '1:46:00 PM'
-            assert babel.format_timedelta(delta) == '1 week'
-            assert babel.format_timedelta(delta, threshold=1) == '6 days'
-
-        with app.test_request_context():
-            app.config['BABEL_DEFAULT_TIMEZONE'] = 'Europe/Vienna'
-            assert babel.format_datetime(d) == 'Apr 12, 2010, 3:46:00 PM'
-            assert babel.format_date(d) == 'Apr 12, 2010'
-            assert babel.format_time(d) == '3:46:00 PM'
-
-        with app.test_request_context():
-            app.config['BABEL_DEFAULT_LOCALE'] = 'de_DE'
-            assert babel.format_datetime(d, 'long') == \
-                '12. April 2010 um 15:46:00 MESZ'
-
-    def test_init_app(self):
-        b = babel.Babel()
-        app = flask.Flask(__name__)
-        b.init_app(app)
-        d = datetime(2010, 4, 12, 13, 46)
-
-        with app.test_request_context():
-            assert babel.format_datetime(d) == 'Apr 12, 2010, 1:46:00 PM'
-            assert babel.format_date(d) == 'Apr 12, 2010'
-            assert babel.format_time(d) == '1:46:00 PM'
-
-        with app.test_request_context():
-            app.config['BABEL_DEFAULT_TIMEZONE'] = 'Europe/Vienna'
-            assert babel.format_datetime(d) == 'Apr 12, 2010, 3:46:00 PM'
-            assert babel.format_date(d) == 'Apr 12, 2010'
-            assert babel.format_time(d) == '3:46:00 PM'
-
-        with app.test_request_context():
-            app.config['BABEL_DEFAULT_LOCALE'] = 'de_DE'
-            assert babel.format_datetime(d, 'long') == \
-                '12. April 2010 um 15:46:00 MESZ'
-
-    def test_custom_formats(self):
-        app = flask.Flask(__name__)
-        app.config.update(
-            BABEL_DEFAULT_LOCALE='en_US',
-            BABEL_DEFAULT_TIMEZONE='Pacific/Johnston'
-        )
-        b = babel.Babel(app)
-        b.date_formats['datetime'] = 'long'
-        b.date_formats['datetime.long'] = 'MMMM d, yyyy h:mm:ss a'
-        d = datetime(2010, 4, 12, 13, 46)
-
-        with app.test_request_context():
-            assert babel.format_datetime(d) == 'April 12, 2010 3:46:00 AM'
-
-    def test_custom_locale_selector(self):
-        app = flask.Flask(__name__)
-        b = babel.Babel(app)
-        d = datetime(2010, 4, 12, 13, 46)
-
-        the_timezone = 'UTC'
-        the_locale = 'en_US'
-
-        @b.localeselector
-        def select_locale():
-            return the_locale
-
-        @b.timezoneselector
-        def select_timezone():
-            return the_timezone
-
-        with app.test_request_context():
-            assert babel.format_datetime(d) == 'Apr 12, 2010, 1:46:00 PM'
-
-        the_locale = 'de_DE'
-        the_timezone = 'Europe/Vienna'
-
-        with app.test_request_context():
-            assert babel.format_datetime(d) == '12.04.2010, 15:46:00'
-
-    def test_refreshing(self):
-        app = flask.Flask(__name__)
-        babel.Babel(app)
-        d = datetime(2010, 4, 12, 13, 46)
-        with app.test_request_context():
-            assert babel.format_datetime(d) == 'Apr 12, 2010, 1:46:00 PM'
-            app.config['BABEL_DEFAULT_TIMEZONE'] = 'Europe/Vienna'
-            babel.refresh()
-            assert babel.format_datetime(d) == 'Apr 12, 2010, 3:46:00 PM'
-
-    def test_force_locale(self):
-        app = flask.Flask(__name__)
-        b = babel.Babel(app)
-
-        @b.localeselector
-        def select_locale():
-            return 'de_DE'
-
-        with app.test_request_context():
-            assert str(babel.get_locale()) == 'de_DE'
-            with babel.force_locale('en_US'):
-                assert str(babel.get_locale()) == 'en_US'
-            assert str(babel.get_locale()) == 'de_DE'
-
-    def test_force_locale_with_threading(self):
-        app = flask.Flask(__name__)
-        b = babel.Babel(app)
-
-        @b.localeselector
-        def select_locale():
-            return 'de_DE'
-
-        semaphore = Semaphore(value=0)
-
-        def first_request():
-            with app.test_request_context():
-                with babel.force_locale('en_US'):
-                    assert str(babel.get_locale()) == 'en_US'
-                    semaphore.acquire()
-
-        thread = Thread(target=first_request)
-        thread.start()
-
-        try:
-            with app.test_request_context():
-                assert str(babel.get_locale()) == 'de_DE'
-        finally:
-            semaphore.release()
-            thread.join()
-
-    def test_refresh_during_force_locale(self):
-        app = flask.Flask(__name__)
-        b = babel.Babel(app)
-
-        @b.localeselector
-        def select_locale():
-            return 'de_DE'
-
-        with app.test_request_context():
-            with babel.force_locale('en_US'):
-                assert str(babel.get_locale()) == 'en_US'
-                babel.refresh()
-                assert str(babel.get_locale()) == 'en_US'
-
-
-class NumberFormattingTestCase(unittest.TestCase):
-
-    def test_basics(self):
-        app = flask.Flask(__name__)
-        babel.Babel(app)
-        n = 1099
-
-        with app.test_request_context():
-            assert babel.format_number(n) == u'1,099'
-            assert babel.format_decimal(Decimal('1010.99')) == u'1,010.99'
-            assert babel.format_currency(n, 'USD') == '$1,099.00'
-            assert babel.format_percent(0.19) == '19%'
-            assert babel.format_scientific(10000) == u'1E4'
-
-
-class GettextTestCase(unittest.TestCase):
-
-    def test_basics(self):
-        app = flask.Flask(__name__)
-        babel.Babel(app, default_locale='de_DE')
-
-        with app.test_request_context():
-            assert gettext(u'Hello %(name)s!', name='Peter') == 'Hallo Peter!'
-            assert ngettext(u'%(num)s Apple', u'%(num)s Apples', 3) == \
-                u'3 Äpfel'
-            assert ngettext(u'%(num)s Apple', u'%(num)s Apples', 1) == \
-                u'1 Apfel'
-
-    def test_template_basics(self):
-        app = flask.Flask(__name__)
-        babel.Babel(app, default_locale='de_DE')
-
-        t = lambda x: flask.render_template_string('{{ %s }}' % x)
-
-        with app.test_request_context():
-            assert t("gettext('Hello %(name)s!', name='Peter')") == \
-                u'Hallo Peter!'
-            assert t("ngettext('%(num)s Apple', '%(num)s Apples', 3)") == \
-                u'3 Äpfel'
-            assert t("ngettext('%(num)s Apple', '%(num)s Apples', 1)") == \
-                u'1 Apfel'
-            assert flask.render_template_string('''
-                {% trans %}Hello {{ name }}!{% endtrans %}
-            ''', name='Peter').strip() == 'Hallo Peter!'
-            assert flask.render_template_string('''
-                {% trans num=3 %}{{ num }} Apple
-                {%- pluralize %}{{ num }} Apples{% endtrans %}
-            ''', name='Peter').strip() == u'3 Äpfel'
-
-    def test_lazy_gettext(self):
-        app = flask.Flask(__name__)
-        babel.Babel(app, default_locale='de_DE')
-        yes = lazy_gettext(u'Yes')
-        with app.test_request_context():
-            assert text_type(yes) == 'Ja'
-            assert yes.__html__() == 'Ja'
-        app.config['BABEL_DEFAULT_LOCALE'] = 'en_US'
-        with app.test_request_context():
-            assert text_type(yes) == 'Yes'
-            assert yes.__html__() == 'Yes'
-
-    def test_lazy_ngettext(self):
-        app = flask.Flask(__name__)
-        babel.Babel(app, default_locale='de_DE')
-        one_apple = lazy_ngettext(u'%(num)s Apple', u'%(num)s Apples', 1)
-        with app.test_request_context():
-            assert text_type(one_apple) == '1 Apfel'
-            assert one_apple.__html__() == '1 Apfel'
-        two_apples = lazy_ngettext(u'%(num)s Apple', u'%(num)s Apples', 2)
-        with app.test_request_context():
-            assert text_type(two_apples) == u'2 Äpfel'
-            assert two_apples.__html__() == u'2 Äpfel'
-
-    def test_list_translations(self):
-        app = flask.Flask(__name__)
-        b = babel.Babel(app, default_locale='de_DE')
-        translations = b.list_translations()
-        assert len(translations) == 1
-        assert str(translations[0]) == 'de'
-
-    def test_no_formatting(self):
-        """
-        Ensure we don't format strings unless a variable is passed.
-        """
-        app = flask.Flask(__name__)
-        babel.Babel(app)
-
-        with app.test_request_context():
-            assert gettext(u'Test %s') == u'Test %s'
-            assert gettext(u'Test %(name)s', name=u'test') == u'Test test'
-            assert gettext(u'Test %s') % 'test' == u'Test test'
-
-
-if __name__ == '__main__':
-    unittest.main()
diff --git a/tests/translations/de/LC_MESSAGES/test.mo b/tests/translations/de/LC_MESSAGES/test.mo
new file mode 100644
index 0000000..4ccc9e7
Binary files /dev/null and b/tests/translations/de/LC_MESSAGES/test.mo differ
diff --git a/tests/translations/de/LC_MESSAGES/test.po b/tests/translations/de/LC_MESSAGES/test.po
new file mode 100644
index 0000000..4fd47ec
--- /dev/null
+++ b/tests/translations/de/LC_MESSAGES/test.po
@@ -0,0 +1,23 @@
+# Translations template for PROJECT.
+# Copyright (C) 2010 ORGANIZATION
+# This file is distributed under the same license as the PROJECT project.
+# FIRST AUTHOR <EMAIL@ADDRESS>, 2010.
+#
+msgid ""
+msgstr ""
+"Project-Id-Version: PROJECT VERSION\n"
+"Report-Msgid-Bugs-To: EMAIL@ADDRESS\n"
+"POT-Creation-Date: 2010-05-30 12:56+0200\n"
+"PO-Revision-Date: 2012-04-11 15:18+0200\n"
+"Last-Translator: Serge S. Koval <serge.koval+github@gmail.com>\n"
+"Language-Team: LANGUAGE <LL@li.org>\n"
+"MIME-Version: 1.0\n"
+"Content-Type: text/plain; charset=utf-8\n"
+"Content-Transfer-Encoding: 8bit\n"
+"Generated-By: Babel 0.9.5\n"
+
+#: tests.py:94
+#, python-format
+msgid "first"
+msgstr "erste"
+
diff --git a/tox.ini b/tox.ini
index dd25176..200c161 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,7 +1,10 @@
 [tox]
-envlist = py27, py36
+envlist = py{38,37,36,27}
 
 [testenv]
-deps = pytz>=2013a
+deps =
+    pytz>=2013a
+    pytest
+    pytest-mock
 whitelist_externals = make
-commands = make test
+commands = pytest