Fix directive test on FreeBSD

src/xdoctest/directive.py

@@ -120,21 +120,26 @@
 
 Example:
     >>> import sys
+    >>> plat = sys.platform
     >>> count = 0
     >>> # xdoctest: +REQUIRES(WIN32)
-    >>> assert sys.platform.startswith('win32')
+    >>> assert plat.startswith('win32'), 'this only runs on windows'
     >>> count += 1
     >>> # xdoctest: -REQUIRES(WIN32)
     >>> # xdoctest: +REQUIRES(LINUX)
-    >>> assert sys.platform.startswith('linux')
+    >>> assert plat.startswith('linux'), 'this only runs on linux'
     >>> count += 1
     >>> # xdoctest: -REQUIRES(LINUX)
     >>> # xdoctest: +REQUIRES(DARWIN)
-    >>> assert sys.platform.startswith('darwin')
+    >>> assert plat.startswith('darwin'), 'this only runs on osx'
     >>> count += 1
     >>> # xdoctest: -REQUIRES(DARWIN)
     >>> print(count)
-    >>> assert count == 1, 'Exactly one of the above parts should have run'
+    >>> import sys
+    >>> if any(plat.startswith(n) for n in {'linux', 'win32', 'darwin'}):
+    >>>     assert count == 1, 'Exactly one of the above parts should have run'
+    >>> else:
+    >>>     assert count == 0, 'Nothing should have run on plat={}'.format(plat)
     >>> # xdoctest: +REQUIRES(--verbose)
     >>> print('This is only printed if you run with --verbose')
 
@@ -705,7 +710,8 @@ def _is_requires_satisfied(arg, argv=None, environ=None):
         >>>     _is_requires_satisfied('env:BAR>=1', argv=[], environ={'BAR': '0'})
     """
     # TODO: add python version options
-    SYS_PLATFORM_TAGS = ['win32', 'linux', 'darwin', 'cywgin']
+    # https://docs.python.org/3/library/sys.html#sys.platform
+    SYS_PLATFORM_TAGS = ['win32', 'linux', 'darwin', 'cywgin', 'aix', 'freebsd']
     OS_NAME_TAGS = ['posix', 'nt', 'java']
     PY_IMPL_TAGS = ['cpython', 'ironpython', 'jython', 'pypy']
     # TODO: tox tags: https://tox.readthedocs.io/en/latest/example/basic.html