Consider plugins loaded by PYTEST_PLUGINS for assertion rewrite

Fix pytest-dev#2185

CHANGELOG.rst

@@ -6,6 +6,10 @@
 * pytest no longer recognizes coroutine functions as yield tests (`#2129`_).
   Thanks to `@malinoff`_ for the PR.
 
+* Plugins loaded by the ``PYTEST_PLUGINS`` environment variable are now automatically
+  considered for assertion rewriting (`#2185`_).
+  Thanks `@nicoddemus`_ for the PR.
+
 * Improve error message when pytest.warns fails (`#2150`_). The type(s) of the
   expected warnings and the list of caught warnings is added to the
   error message. Thanks `@lesteve`_ for the PR.
@@ -23,6 +27,7 @@
 .. _#2129: https://github.com/pytest-dev/pytest/issues/2129
 .. _#2148: https://github.com/pytest-dev/pytest/issues/2148
 .. _#2150: https://github.com/pytest-dev/pytest/issues/2150
+.. _#2185: https://github.com/pytest-dev/pytest/issues/2185
 
 
 3.0.5 (2016-12-05)

_pytest/config.py

@@ -399,13 +399,15 @@ def consider_conftest(self, conftestmodule):
             self.consider_module(conftestmodule)
 
     def consider_env(self):
-        self._import_plugin_specs(os.environ.get("PYTEST_PLUGINS"))
+        specs = os.environ.get("PYTEST_PLUGINS")
+        if specs:
+            plugins = specs.split(',')
+            self._import_plugin_specs(plugins)
 
     def consider_module(self, mod):
         plugins = getattr(mod, 'pytest_plugins', [])
         if isinstance(plugins, str):
             plugins = [plugins]
-        self.rewrite_hook.mark_rewrite(*plugins)
         self._import_plugin_specs(plugins)
 
     def _import_plugin_specs(self, spec):
@@ -427,6 +429,7 @@ def import_plugin(self, modname):
             importspec = "_pytest." + modname
         else:
             importspec = modname
+        self.rewrite_hook.mark_rewrite(modname)
         try:
             __import__(importspec)
         except ImportError as e:

testing/test_assertrewrite.py

@@ -682,7 +682,7 @@ def test_remember_rewritten_modules(self, pytestconfig, testdir, monkeypatch):
         hook.mark_rewrite('test_remember_rewritten_modules')
         assert warnings == []
 
-    def test_rewrite_warning_using_pytest_plugins(self, testdir, monkeypatch):
+    def test_rewrite_warning_using_pytest_plugins(self, testdir):
         testdir.makepyfile(**{
             'conftest.py': "pytest_plugins = ['core', 'gui', 'sci']",
             'core.py': "",
@@ -695,6 +695,22 @@ def test_rewrite_warning_using_pytest_plugins(self, testdir, monkeypatch):
         result.stdout.fnmatch_lines(['*= 1 passed in *=*'])
         assert 'pytest-warning summary' not in result.stdout.str()
 
+    def test_rewrite_warning_using_pytest_plugins_env_var(self, testdir, monkeypatch):
+        monkeypatch.setenv('PYTEST_PLUGINS', 'plugin')
+        testdir.makepyfile(**{
+            'plugin.py': "",
+            'test_rewrite_warning_using_pytest_plugins_env_var.py': """
+                import plugin
+                pytest_plugins = ['plugin']
+                def test():
+                    pass
+            """,
+        })
+        testdir.chdir()
+        result = testdir.runpytest_subprocess()
+        result.stdout.fnmatch_lines(['*= 1 passed in *=*'])
+        assert 'pytest-warning summary' not in result.stdout.str()
+
 
 class TestAssertionRewriteHookDetails(object):
     def test_loader_is_package_false_for_module(self, testdir):