Rewrite asserts in test-modules loaded very early in the startup

Also now match modules which start with any of the names registered
using register_assert_rewrite as discussed in #1787

Fix #1784

_pytest/assertion/__init__.py

@@ -31,10 +31,11 @@ def pytest_namespace():
 def register_assert_rewrite(*names):
     """Register a module name to be rewritten on import.
 
-    This function will make sure that the module will get it's assert
-    statements rewritten when it is imported.  Thus you should make
-    sure to call this before the module is actually imported, usually
-    in your __init__.py if you are a plugin using a package.
+    This function will make sure that this module or all modules inside
+    the package will get their assert statements rewritten.
+    Thus you should make sure to call this before the module is
+    actually imported, usually in your __init__.py if you are a plugin
+    using a package.
     """
     for hook in sys.meta_path:
         if isinstance(hook, rewrite.AssertionRewritingHook):

_pytest/assertion/rewrite.py

@@ -11,6 +11,7 @@ import re
 import struct
 import sys
 import types
+from fnmatch import fnmatch
 
 import py
 from _pytest.assertion import util
@@ -144,28 +145,29 @@ class AssertionRewritingHook(object):
         if fn_pypath.basename == 'conftest.py':
             state.trace("rewriting conftest file: %r" % (fn,))
             return True
-        elif self.session is not None:
+
+        if self.session is not None:
             if self.session.isinitpath(fn):
                 state.trace("matched test file (was specified on cmdline): %r" %
                             (fn,))
                 return True
-            else:
-                # modules not passed explicitly on the command line are only
-                # rewritten if they match the naming convention for test files
-                session = self.session  # avoid a cycle here
-                self.session = None
-                try:
-                    for pat in self.fnpats:
-                        if fn_pypath.fnmatch(pat):
-                            state.trace("matched test file %r" % (fn,))
-                            return True
-                finally:
-                    self.session = session
-                    del session
-        else:
-            for marked in self._must_rewrite:
-                if marked.startswith(name):
-                    return True
+
+        # modules not passed explicitly on the command line are only
+        # rewritten if they match the naming convention for test files
+        for pat in self.fnpats:
+            # use fnmatch instead of fn_pypath.fnmatch because the
+            # latter might trigger an import to fnmatch.fnmatch
+            # internally, which would cause this method to be
+            # called recursively
+            if fnmatch(fn_pypath.basename, pat):
+                state.trace("matched test file %r" % (fn,))
+                return True
+
+        for marked in self._must_rewrite:
+            if name.startswith(marked):
+                state.trace("matched marked file %r (from %r)" % (name, marked))
+                return True
+
         return False
 
     def mark_rewrite(self, *names):

testing/test_assertrewrite.py

@@ -533,6 +533,16 @@ def test_rewritten():
         hook.mark_rewrite('_pytest')
         assert '_pytest' in warnings[0][1]
 
+    def test_rewrite_module_imported_from_conftest(self, testdir):
+        testdir.makeconftest('''
+            import test_rewrite_module_imported
+        ''')
+        testdir.makepyfile(test_rewrite_module_imported='''
+            def test_rewritten():
+                assert "@py_builtins" in globals()
+        ''')
+        assert testdir.runpytest_subprocess().ret == 0
+
 
 class TestAssertionRewriteHookDetails(object):
     def test_loader_is_package_false_for_module(self, testdir):