Show deselection count before tests are exectued

Fixes #1527

_pytest/terminal.py

@@ -361,13 +361,16 @@ def report_collect(self, final=False):
 
         errors = len(self.stats.get('error', []))
         skipped = len(self.stats.get('skipped', []))
+        deselected = len(self.stats.get('deselected', []))
         if final:
             line = "collected "
         else:
             line = "collecting "
         line += str(self._numcollected) + " item" + ('' if self._numcollected == 1 else 's')
         if errors:
             line += " / %d errors" % errors
+        if deselected:
+            line += " / %d deselected" % deselected
         if skipped:
             line += " / %d skipped" % skipped
         if self.isatty:
@@ -377,6 +380,7 @@ def report_collect(self, final=False):
         else:
             self.write_line(line)
 
+    @pytest.hookimpl(trylast=True)
     def pytest_collection_modifyitems(self):
         self.report_collect(True)
 
@@ -484,7 +488,6 @@ def pytest_sessionfinish(self, exitstatus):
         if exitstatus == EXIT_INTERRUPTED:
             self._report_keyboardinterrupt()
             del self._keyboardinterrupt_memo
-        self.summary_deselected()
         self.summary_stats()
 
     def pytest_keyboard_interrupt(self, excinfo):
@@ -649,11 +652,6 @@ def summary_stats(self):
         if self.verbosity == -1:
             self.write_line(msg, **markup)
 
-    def summary_deselected(self):
-        if 'deselected' in self.stats:
-            self.write_sep("=", "%d tests deselected" % (
-                len(self.stats['deselected'])), bold=True)
-
 
 def repr_pythonversion(v=None):
     if v is None:

changelog/0000.feature

@@ -0,0 +1 @@
+Output item deselection count before tests are run.

testing/test_terminal.py

@@ -431,11 +431,36 @@ def test_three():
                                       )
         result = testdir.runpytest("-k", "test_two:", testpath)
         result.stdout.fnmatch_lines([
+            "collected 3 items / 1 deselected",
             "*test_deselected.py ..*",
-            "=* 1 test*deselected *=",
         ])
         assert result.ret == 0
 
+    def test_show_deselected_items_using_markexpr_before_test_execution(
+            self, testdir):
+        testdir.makepyfile("""
+            import pytest
+
+            @pytest.mark.foo
+            def test_foobar():
+                pass
+
+            @pytest.mark.bar
+            def test_bar():
+                pass
+
+            def test_pass():
+                pass
+        """)
+        result = testdir.runpytest('-m', 'not foo')
+        result.stdout.fnmatch_lines([
+            "collected 3 items / 1 deselected",
+            "*test_show_des*.py ..*",
+            "*= 2 passed, 1 deselected in * =*",
+        ])
+        assert "= 1 deselected =" not in result.stdout.str()
+        assert result.ret == 0
+
     def test_no_skip_summary_if_failure(self, testdir):
         testdir.makepyfile("""
             import pytest