Merge pull request #3940 from nicoddemus/release-3.8.0

Release 3.8.0

.coveragerc

@@ -1,3 +1,4 @@
 [run]
 source = _pytest,testing
 parallel = 1
+branch = 1

.gitignore

@@ -38,3 +38,6 @@ env/
 .ropeproject
 .idea
 .hypothesis
+.pydevproject
+.project
+.settings

AUTHORS

@@ -73,6 +73,7 @@ Endre Galaczi
 Eric Hunsberger
 Eric Siegerman
 Erik M. Bray
+Fabio Zadrozny
 Feng Ma
 Florian Bruhin
 Floris Bruynooghe

CHANGELOG.rst

@@ -18,6 +18,90 @@ with advance notice in the **Deprecations** section of releases.
 
 .. towncrier release notes start
 
+pytest 3.8.0 (2018-09-05)
+=========================
+
+Deprecations and Removals
+-------------------------
+
+- `#2452 <https://github.com/pytest-dev/pytest/issues/2452>`_: ``Config.warn`` has been deprecated, it should be replaced by calls to the standard ``warnings.warn``.
+
+  ``Node.warn`` now supports two signatures:
+
+  * ``node.warn(PytestWarning("some message"))``: is now the recommended way to call this function. The warning
+    instance must be a ``PytestWarning`` or subclass  instance.
+
+  * ``node.warn("CI", "some message")``: this code/message form is now deprecated and should be converted to
+    the warning instance form above.
+
+  ``RemovedInPytest4Warning`` and ``PytestExperimentalApiWarning`` are now part of the public API and should be accessed
+  using ``pytest.RemovedInPytest4Warning`` and ``pytest.PytestExperimentalApiWarning``.
+
+
+- `#3936 <https://github.com/pytest-dev/pytest/issues/3936>`_: ``@pytest.mark.filterwarnings`` second parameter is no longer regex-escaped,
+  making it possible to actually use regular expressions to check the warning message.
+
+  **Note**: regex-escaping the match string was an implementation oversight that might break test suites which depend
+  on the old behavior.
+
+
+
+Features
+--------
+
+- `#2452 <https://github.com/pytest-dev/pytest/issues/2452>`_: Internal pytest warnings are now issued using the standard ``warnings`` module, making it possible to use
+  the standard warnings filters to manage those warnings. This introduces ``PytestWarning``,
+  ``PytestDeprecationWarning`` and ``RemovedInPytest4Warning`` warning types as part of the public API.
+
+  Consult `the documentation <https://docs.pytest.org/en/latest/warnings.html#internal-pytest-warnings>`_ for more info.
+
+
+- `#2908 <https://github.com/pytest-dev/pytest/issues/2908>`_: ``DeprecationWarning`` and ``PendingDeprecationWarning`` are now shown by default if no other warning filter is
+  configured. This makes pytest more compliant with
+  `PEP-0506 <https://www.python.org/dev/peps/pep-0565/#recommended-filter-settings-for-test-runners>`_. See
+  `the docs <https://docs.pytest.org/en/latest/warnings.html#deprecationwarning-and-pendingdeprecationwarning>`_ for
+  more info.
+
+
+- `#3784 <https://github.com/pytest-dev/pytest/issues/3784>`_: Add option to disable plugin auto-loading.
+
+
+- `#3829 <https://github.com/pytest-dev/pytest/issues/3829>`_: Added the ``count`` option to ``console_output_style`` to enable displaying the progress as a count instead of a percentage.
+
+
+- `#3837 <https://github.com/pytest-dev/pytest/issues/3837>`_: Added support for 'xfailed' and 'xpassed' outcomes to the ``pytester.RunResult.assert_outcomes`` signature.
+
+
+
+Bug Fixes
+---------
+
+- `#3911 <https://github.com/pytest-dev/pytest/issues/3911>`_: Terminal writer now takes into account unicode character width when writing out progress.
+
+
+- `#3913 <https://github.com/pytest-dev/pytest/issues/3913>`_: Pytest now returns with correct exit code (EXIT_USAGEERROR, 4) when called with unknown arguments.
+
+
+- `#3918 <https://github.com/pytest-dev/pytest/issues/3918>`_: Improve performance of assertion rewriting.
+
+
+
+Improved Documentation
+----------------------
+
+- `#3566 <https://github.com/pytest-dev/pytest/issues/3566>`_: Added a blurb in usage.rst for the usage of -r flag which is used to show an extra test summary info.
+
+
+- `#3907 <https://github.com/pytest-dev/pytest/issues/3907>`_: Corrected type of the exceptions collection passed to ``xfail``: ``raises`` argument accepts a ``tuple`` instead of ``list``.
+
+
+
+Trivial/Internal Changes
+------------------------
+
+- `#3853 <https://github.com/pytest-dev/pytest/issues/3853>`_: Removed ``"run all (no recorded failures)"`` message printed with ``--failed-first`` and ``--last-failed`` when there are no failed tests.
+
+
 pytest 3.7.4 (2018-08-29)
 =========================
 

appveyor.yml

@@ -15,7 +15,7 @@ environment:
   - TOXENV: "py35"
   - TOXENV: "py36"
   - TOXENV: "py37"
-#  - TOXENV: "pypy" reenable when we are able to provide a scandir wheel or build scandir
+  - TOXENV: "pypy"
   - TOXENV: "py27-pexpect"
   - TOXENV: "py27-xdist"
   - TOXENV: "py27-trial"

changelog/2452.feature.rst

@@ -1,5 +0,0 @@
-Internal pytest warnings are now issued using the standard ``warnings`` module, making it possible to use
-the standard warnings filters to manage those warnings. This introduces ``PytestWarning``,
-``PytestDeprecationWarning`` and ``RemovedInPytest4Warning`` warning types as part of the public API.
-
-Consult `the documentation <https://docs.pytest.org/en/latest/warnings.html#internal-pytest-warnings>`_ for more info.

changelog/2452.removal.rst

@@ -1,12 +0,0 @@
-``Config.warn`` has been deprecated, it should be replaced by calls to the standard ``warnings.warn``.
-
-``Node.warn`` now supports two signatures:
-
-* ``node.warn(PytestWarning("some message"))``: is now the recommended way to call this function. The warning
-  instance must be a ``PytestWarning`` or subclass  instance.
-
-* ``node.warn("CI", "some message")``: this code/message form is now deprecated and should be converted to
-  the warning instance form above.
-
-``RemovedInPytest4Warning`` and ``PytestExperimentalApiWarning`` are now part of the public API and should be accessed
-using ``pytest.RemovedInPytest4Warning`` and ``pytest.PytestExperimentalApiWarning``.

changelog/2908.feature.rst

@@ -1,5 +0,0 @@
-``DeprecationWarning`` and ``PendingDeprecationWarning`` are now shown by default if no other warning filter is
-configured. This makes pytest more compliant with
-`PEP-0506 <https://www.python.org/dev/peps/pep-0565/#recommended-filter-settings-for-test-runners>`_. See
-`the docs <https://docs.pytest.org/en/latest/warnings.html#deprecationwarning-and-pendingdeprecationwarning>`_ for
-more info.

changelog/3784.feature.rst

@@ -1 +0,0 @@
-Add option to disable plugin auto-loading.

changelog/3829.feature.rst

@@ -1 +0,0 @@
-Added the ``count`` option to ``console_output_style`` to enable displaying the progress as a count instead of a percentage.

changelog/3837.feature.rst

@@ -1 +0,0 @@
-Added support for 'xfailed' and 'xpassed' outcomes to the ``pytester.RunResult.assert_outcomes`` signature.

changelog/3853.trivial.rst

@@ -1 +0,0 @@
-Removed ``"run all (no recorded failures)"`` message printed with ``--failed-first`` and ``--last-failed`` when there are no failed tests.

changelog/3907.doc.rst

@@ -1 +0,0 @@
-Corrected type of the exceptions collection passed to ``xfail``: ``raises`` argument accepts a ``tuple`` instead of ``list``.

changelog/3913.bugfix.rst

@@ -1 +0,0 @@
-Pytest now returns with correct exit code (EXIT_USAGEERROR, 4) when called with unknown arguments.

changelog/3936.removal.rst

@@ -1,5 +0,0 @@
-``@pytest.mark.filterwarnings`` second parameter is no longer regex-escaped,
-making it possible to actually use regular expressions to check the warning message.
-
-**Note**: regex-escaping the match string was an implementation oversight that might break test suites which depend
-on the old behavior.

doc/en/announce/index.rst

@@ -6,6 +6,7 @@ Release announcements
    :maxdepth: 2
 
 
+   release-3.8.0
    release-3.7.4
    release-3.7.3
    release-3.7.2

doc/en/announce/release-3.8.0.rst

@@ -0,0 +1,38 @@
+pytest-3.8.0
+=======================================
+
+The pytest team is proud to announce the 3.8.0 release!
+
+pytest is a mature Python testing tool with more than a 2000 tests
+against itself, passing on many different interpreters and platforms.
+
+This release contains a number of bugs fixes and improvements, so users are encouraged
+to take a look at the CHANGELOG:
+
+    https://docs.pytest.org/en/latest/changelog.html
+
+For complete documentation, please visit:
+
+    https://docs.pytest.org/en/latest/
+
+As usual, you can upgrade from pypi via:
+
+    pip install -U pytest
+
+Thanks to all who contributed to this release, among them:
+
+* Anthony Sottile
+* Bruno Oliveira
+* CrazyMerlyn
+* Daniel Hahler
+* Fabio Zadrozny
+* Jeffrey Rackauckas
+* Ronny Pfannschmidt
+* Virgil Dupras
+* dhirensr
+* hoefling
+* wim glenn
+
+
+Happy testing,
+The Pytest Development Team

doc/en/conf.py

@@ -329,7 +329,7 @@ texinfo_documents = [
 
 
 # Example configuration for intersphinx: refer to the Python standard library.
-intersphinx_mapping = {"python": ("http://docs.python.org/3", None)}
+intersphinx_mapping = {"python": ("https://docs.python.org/3", None)}
 
 
 def setup(app):

doc/en/example/reportingdemo.rst

@@ -613,9 +613,9 @@ get on the terminal - we are working on that)::
 
     failure_demo.py:261: AssertionError
     ============================= warnings summary =============================
-    <undetermined location>
+    $REGENDOC_TMPDIR/assertion/failure_demo.py:24: RemovedInPytest4Warning: Metafunc.addcall is deprecated and scheduled to be removed in pytest 4.0.
-      Metafunc.addcall is deprecated and scheduled to be removed in pytest 4.0.
+    Please use Metafunc.parametrize instead.
-      Please use Metafunc.parametrize instead.
+      metafunc.addcall(funcargs=dict(param1=3, param2=6))
 
     -- Docs: https://docs.pytest.org/en/latest/warnings.html
     ================== 42 failed, 1 warnings in 0.12 seconds ===================

doc/en/talks.rst

@@ -14,6 +14,9 @@ Talks and Tutorials
 Books
 ---------------------------------------------
 
+- `pytest Quick Start Guide, by Bruno Oliveira (2018)
+  <https://www.packtpub.com/web-development/pytest-quick-start-guide>`_.
+
 - `Python Testing with pytest, by Brian Okken (2017)
   <https://pragprog.com/book/bopytest/python-testing-with-pytest>`_.
 

doc/en/usage.rst

@@ -140,6 +140,49 @@ will be shown (because KeyboardInterrupt is caught by pytest). By using this
 option you make sure a trace is shown.
 
 
+.. _`pytest.detailed_failed_tests_usage`:
+
+Detailed summary report
+-----------------------
+
+.. versionadded:: 2.9
+
+The ``-r`` flag can be used to display test results summary at the end of the test session,
+making it easy in large test suites to get a clear picture of all failures, skips, xfails, etc.
+
+Example::
+
+    $ pytest -ra
+    =========================== test session starts ============================
+    platform linux -- Python 3.x.y, pytest-3.x.y, py-1.x.y, pluggy-0.x.y
+    rootdir: $REGENDOC_TMPDIR, inifile:
+    collected 0 items
+
+    ======================= no tests ran in 0.12 seconds =======================
+
+The ``-r`` options accepts a number of characters after it, with ``a`` used above meaning "all except passes".
+
+Here is the full list of available characters that can be used:
+
+ - ``f`` - failed
+ - ``E`` - error
+ - ``s`` - skipped
+ - ``x`` - xfailed
+ - ``X`` - xpassed
+ - ``p`` - passed
+ - ``P`` - passed with output
+ - ``a`` - all except ``pP``
+
+More than one character can be used, so for example to only see failed and skipped tests, you can execute::
+
+    $ pytest -rfs
+    =========================== test session starts ============================
+    platform linux -- Python 3.x.y, pytest-3.x.y, py-1.x.y, pluggy-0.x.y
+    rootdir: $REGENDOC_TMPDIR, inifile:
+    collected 0 items
+
+    ======================= no tests ran in 0.12 seconds =======================
+
 .. _pdb-option:
 
 Dropping to PDB_ (Python Debugger) on failures

doc/en/warnings.rst

@@ -29,9 +29,8 @@ Running pytest now produces this output::
     test_show_warnings.py .                                              [100%]
 
     ============================= warnings summary =============================
-    test_show_warnings.py::test_one
+    $REGENDOC_TMPDIR/test_show_warnings.py:4: UserWarning: api v1, should use functions from v2
-      $REGENDOC_TMPDIR/test_show_warnings.py:4: UserWarning: api v1, should use functions from v2
+      warnings.warn(UserWarning("api v1, should use functions from v2"))
-        warnings.warn(UserWarning("api v1, should use functions from v2"))
 
     -- Docs: https://docs.pytest.org/en/latest/warnings.html
     =================== 1 passed, 1 warnings in 0.12 seconds ===================
@@ -354,15 +353,13 @@ defines an ``__init__`` constructor, as this prevents the class from being insta
 ::
 
     $ pytest test_pytest_warnings.py -q
-    ======================================== warnings summary =========================================
-    test_pytest_warnings.py:1
-      $REGENDOC_TMPDIR/test_pytest_warnings.py:1: PytestWarning: cannot collect test class 'Test' because it has a __init__ constructor
-        class Test:
-
-    -- Docs: http://doc.pytest.org/en/latest/warnings.html
-    1 warnings in 0.01 seconds
 
+    ============================= warnings summary =============================
+    $REGENDOC_TMPDIR/test_pytest_warnings.py:1: PytestWarning: cannot collect test class 'Test' because it has a __init__ constructor
+      class Test:
 
+    -- Docs: https://docs.pytest.org/en/latest/warnings.html
+    1 warnings in 0.12 seconds
 
 These warnings might be filtered using the same builtin mechanisms used to filter other types of warnings.
 

doc/en/writing_plugins.rst

@@ -418,9 +418,8 @@ additionally it is possible to copy examples for a example folder before running
     test_example.py ..                                                   [100%]
 
     ============================= warnings summary =============================
-    test_example.py::test_plugin
+    $REGENDOC_TMPDIR/test_example.py:4: PytestExperimentalApiWarning: testdir.copy_example is an experimental api that may change over time
-      $REGENDOC_TMPDIR/test_example.py:4: PytestExperimentalApiWarning: testdir.copy_example is an experimental api that may change over time
+      testdir.copy_example("test_example.py")
-        testdir.copy_example("test_example.py")
 
     -- Docs: https://docs.pytest.org/en/latest/warnings.html
     =================== 2 passed, 1 warnings in 0.12 seconds ===================

setup.py

@@ -59,7 +59,7 @@ def get_environment_marker_support_level():
 def main():
     extras_require = {}
     install_requires = [
-        "py>=1.5.0",
+        "py>=1.5.0",  # if py gets upgrade to >=1.6, remove _width_of_current_line in terminal.py
         "six>=1.10.0",
         "setuptools",
         "attrs>=17.4.0",

src/_pytest/assertion/rewrite.py

@@ -67,14 +67,24 @@ class AssertionRewritingHook(object):
         # flag to guard against trying to rewrite a pyc file while we are already writing another pyc file,
         # which might result in infinite recursion (#3506)
         self._writing_pyc = False
+        self._basenames_to_check_rewrite = {"conftest"}
+        self._marked_for_rewrite_cache = {}
+        self._session_paths_checked = False
 
     def set_session(self, session):
         self.session = session
+        self._session_paths_checked = False
+
+    def _imp_find_module(self, name, path=None):
+        """Indirection so we can mock calls to find_module originated from the hook during testing"""
+        return imp.find_module(name, path)
 
     def find_module(self, name, path=None):
         if self._writing_pyc:
             return None
         state = self.config._assertstate
+        if self._early_rewrite_bailout(name, state):
+            return None
         state.trace("find_module called for: %s" % name)
         names = name.rsplit(".", 1)
         lastname = names[-1]
@@ -87,7 +97,7 @@ class AssertionRewritingHook(object):
                 pth = path[0]
         if pth is None:
             try:
-                fd, fn, desc = imp.find_module(lastname, path)
+                fd, fn, desc = self._imp_find_module(lastname, path)
             except ImportError:
                 return None
             if fd is not None:
@@ -166,6 +176,44 @@ class AssertionRewritingHook(object):
         self.modules[name] = co, pyc
         return self
 
+    def _early_rewrite_bailout(self, name, state):
+        """
+        This is a fast way to get out of rewriting modules. Profiling has
+        shown that the call to imp.find_module (inside of the find_module
+        from this class) is a major slowdown, so, this method tries to
+        filter what we're sure won't be rewritten before getting to it.
+        """
+        if self.session is not None and not self._session_paths_checked:
+            self._session_paths_checked = True
+            for path in self.session._initialpaths:
+                # Make something as c:/projects/my_project/path.py ->
+                #     ['c:', 'projects', 'my_project', 'path.py']
+                parts = str(path).split(os.path.sep)
+                # add 'path' to basenames to be checked.
+                self._basenames_to_check_rewrite.add(os.path.splitext(parts[-1])[0])
+
+        # Note: conftest already by default in _basenames_to_check_rewrite.
+        parts = name.split(".")
+        if parts[-1] in self._basenames_to_check_rewrite:
+            return False
+
+        # For matching the name it must be as if it was a filename.
+        parts[-1] = parts[-1] + ".py"
+        fn_pypath = py.path.local(os.path.sep.join(parts))
+        for pat in self.fnpats:
+            # if the pattern contains subdirectories ("tests/**.py" for example) we can't bail out based
+            # on the name alone because we need to match against the full path
+            if os.path.dirname(pat):
+                return False
+            if fn_pypath.fnmatch(pat):
+                return False
+
+        if self._is_marked_for_rewrite(name, state):
+            return False
+
+        state.trace("early skip of rewriting module: %s" % (name,))
+        return True
+
     def _should_rewrite(self, name, fn_pypath, state):
         # always rewrite conftest files
         fn = str(fn_pypath)
@@ -185,12 +233,20 @@ class AssertionRewritingHook(object):
                 state.trace("matched test file %r" % (fn,))
                 return True
 
-        for marked in self._must_rewrite:
+        return self._is_marked_for_rewrite(name, state)
-            if name == marked or name.startswith(marked + "."):
-                state.trace("matched marked file %r (from %r)" % (name, marked))
-                return True
 
-        return False
+    def _is_marked_for_rewrite(self, name, state):
+        try:
+            return self._marked_for_rewrite_cache[name]
+        except KeyError:
+            for marked in self._must_rewrite:
+                if name == marked or name.startswith(marked + "."):
+                    state.trace("matched marked file %r (from %r)" % (name, marked))
+                    self._marked_for_rewrite_cache[name] = True
+                    return True
+
+            self._marked_for_rewrite_cache[name] = False
+            return False
 
     def mark_rewrite(self, *names):
         """Mark import names as needing to be rewritten.
@@ -207,6 +263,7 @@ class AssertionRewritingHook(object):
             ):
                 self._warn_already_imported(name)
         self._must_rewrite.update(names)
+        self._marked_for_rewrite_cache.clear()
 
     def _warn_already_imported(self, name):
         from _pytest.warning_types import PytestWarning
@@ -245,7 +302,7 @@ class AssertionRewritingHook(object):
 
     def is_package(self, name):
         try:
-            fd, fn, desc = imp.find_module(name)
+            fd, fn, desc = self._imp_find_module(name)
         except ImportError:
             return False
         if fd is not None:

src/_pytest/config/__init__.py

@@ -51,6 +51,8 @@ def main(args=None, plugins=None):
     :arg plugins: list of plugin objects to be auto-registered during
                   initialization.
     """
+    from _pytest.main import EXIT_USAGEERROR
+
     try:
         try:
             config = _prepareconfig(args, plugins)
@@ -69,7 +71,7 @@ def main(args=None, plugins=None):
         tw = py.io.TerminalWriter(sys.stderr)
         for msg in e.args:
             tw.line("ERROR: {}\n".format(msg), red=True)
-        return 4
+        return EXIT_USAGEERROR
 
 
 class cmdline(object):  # compatibility namespace

src/_pytest/main.py

@@ -383,6 +383,7 @@ class Session(nodes.FSCollector):
         self.trace = config.trace.root.get("collection")
         self._norecursepatterns = config.getini("norecursedirs")
         self.startdir = py.path.local()
+        self._initialpaths = frozenset()
         # Keep track of any collected nodes in here, so we don't duplicate fixtures
         self._node_cache = {}
 
@@ -441,13 +442,14 @@ class Session(nodes.FSCollector):
         self.trace("perform_collect", self, args)
         self.trace.root.indent += 1
         self._notfound = []
-        self._initialpaths = set()
+        initialpaths = []
         self._initialparts = []
         self.items = items = []
         for arg in args:
             parts = self._parsearg(arg)
             self._initialparts.append(parts)
-            self._initialpaths.add(parts[0])
+            initialpaths.append(parts[0])
+        self._initialpaths = frozenset(initialpaths)
         rep = collect_one_node(self)
         self.ihook.pytest_collectreport(report=rep)
         self.trace.root.indent -= 1
@@ -564,7 +566,6 @@ class Session(nodes.FSCollector):
         """Convert a dotted module name to path.
 
         """
-
         try:
             with _patched_find_module():
                 loader = pkgutil.find_loader(x)

src/_pytest/outcomes.py

@@ -67,13 +67,19 @@ exit.Exception = Exit
 
 
 def skip(msg="", **kwargs):
-    """ skip an executing test with the given message.  Note: it's usually
+    """
-    better to use the pytest.mark.skipif marker to declare a test to be
+    Skip an executing test with the given message.
-    skipped under certain conditions like mismatching platforms or
+
-    dependencies.  See the pytest_skipping plugin for details.
+    This function should be called only during testing (setup, call or teardown) or
+    during collection by using the ``allow_module_level`` flag.
 
     :kwarg bool allow_module_level: allows this function to be called at
         module level, skipping the rest of the module. Default to False.
+
+    .. note::
+        It is better to use the :ref:`pytest.mark.skipif ref` marker when possible to declare a test to be
+        skipped under certain conditions like mismatching platforms or
+        dependencies.
     """
     __tracebackhide__ = True
     allow_module_level = kwargs.pop("allow_module_level", False)
@@ -87,10 +93,12 @@ skip.Exception = Skipped
 
 
 def fail(msg="", pytrace=True):
-    """ explicitly fail a currently-executing test with the given Message.
+    """
+    Explicitly fail an executing test with the given message.
 
-    :arg pytrace: if false the msg represents the full failure information
+    :param str msg: the message to show the user as reason for the failure.
-                  and no python traceback will be reported.
+    :param bool pytrace: if false the msg represents the full failure information and no
+        python traceback will be reported.
     """
     __tracebackhide__ = True
     raise Failed(msg=msg, pytrace=pytrace)
@@ -104,7 +112,15 @@ class XFailed(fail.Exception):
 
 
 def xfail(reason=""):
-    """ xfail an executing test or setup functions with the given reason."""
+    """
+    Imperatively xfail an executing test or setup functions with the given reason.
+
+    This function should be called only during testing (setup, call or teardown).
+
+    .. note::
+        It is better to use the :ref:`pytest.mark.xfail ref` marker when possible to declare a test to be
+        xfailed under certain conditions like known bugs or missing features.
+    """
     __tracebackhide__ = True
     raise XFailed(reason)
 

src/_pytest/terminal.py

@@ -435,10 +435,8 @@ class TerminalReporter(object):
             if last_item:
                 self._write_progress_information_filling_space()
             else:
-                past_edge = (
+                w = self._width_of_current_line
-                    self._tw.chars_on_current_line + progress_length + 1
+                past_edge = w + progress_length + 1 >= self._screen_width
-                    >= self._screen_width
-                )
                 if past_edge:
                     msg = self._get_progress_information_message()
                     self._tw.write(msg + "\n", cyan=True)
@@ -462,10 +460,18 @@ class TerminalReporter(object):
 
     def _write_progress_information_filling_space(self):
         msg = self._get_progress_information_message()
-        fill = " " * (
+        w = self._width_of_current_line
-            self._tw.fullwidth - self._tw.chars_on_current_line - len(msg) - 1
+        fill = self._tw.fullwidth - w - 1
-        )
+        self.write(msg.rjust(fill), cyan=True)
-        self.write(fill + msg, cyan=True)
+
+    @property
+    def _width_of_current_line(self):
+        """Return the width of current line, using the superior implementation of py-1.6 when available"""
+        try:
+            return self._tw.width_of_current_line
+        except AttributeError:
+            # py < 1.6.0
+            return self._tw.chars_on_current_line
 
     def pytest_collection(self):
         if not self.isatty and self.config.option.verbose >= 1:

testing/test_assertrewrite.py

@@ -1106,22 +1106,21 @@ class TestIssue925(object):
 
 
 class TestIssue2121:
-    def test_simple(self, testdir):
+    def test_rewrite_python_files_contain_subdirs(self, testdir):
-        testdir.tmpdir.join("tests/file.py").ensure().write(
+        testdir.makepyfile(
-            """
+            **{
-def test_simple_failure():
+                "tests/file.py": """
-    assert 1 + 1 == 3
+                def test_simple_failure():
-"""
+                    assert 1 + 1 == 3
-        )
-        testdir.tmpdir.join("pytest.ini").write(
-            textwrap.dedent(
                 """
-            [pytest]
+            }
-            python_files = tests/**.py
+        )
-        """
+        testdir.makeini(
-            )
+            """
+                [pytest]
+                python_files = tests/**.py
+            """
         )
-
         result = testdir.runpytest()
         result.stdout.fnmatch_lines("*E*assert (1 + 1) == 3")
 
@@ -1153,3 +1152,83 @@ def test_rewrite_infinite_recursion(testdir, pytestconfig, monkeypatch):
     hook = AssertionRewritingHook(pytestconfig)
     assert hook.find_module("test_foo") is not None
     assert len(write_pyc_called) == 1
+
+
+class TestEarlyRewriteBailout(object):
+    @pytest.fixture
+    def hook(self, pytestconfig, monkeypatch, testdir):
+        """Returns a patched AssertionRewritingHook instance so we can configure its initial paths and track
+        if imp.find_module has been called.
+        """
+        import imp
+
+        self.find_module_calls = []
+        self.initial_paths = set()
+
+        class StubSession(object):
+            _initialpaths = self.initial_paths
+
+            def isinitpath(self, p):
+                return p in self._initialpaths
+
+        def spy_imp_find_module(name, path):
+            self.find_module_calls.append(name)
+            return imp.find_module(name, path)
+
+        hook = AssertionRewritingHook(pytestconfig)
+        # use default patterns, otherwise we inherit pytest's testing config
+        hook.fnpats[:] = ["test_*.py", "*_test.py"]
+        monkeypatch.setattr(hook, "_imp_find_module", spy_imp_find_module)
+        hook.set_session(StubSession())
+        testdir.syspathinsert()
+        return hook
+
+    def test_basic(self, testdir, hook):
+        """
+        Ensure we avoid calling imp.find_module when we know for sure a certain module will not be rewritten
+        to optimize assertion rewriting (#3918).
+        """
+        testdir.makeconftest(
+            """
+            import pytest
+            @pytest.fixture
+            def fix(): return 1
+        """
+        )
+        testdir.makepyfile(test_foo="def test_foo(): pass")
+        testdir.makepyfile(bar="def bar(): pass")
+        foobar_path = testdir.makepyfile(foobar="def foobar(): pass")
+        self.initial_paths.add(foobar_path)
+
+        # conftest files should always be rewritten
+        assert hook.find_module("conftest") is not None
+        assert self.find_module_calls == ["conftest"]
+
+        # files matching "python_files" mask should always be rewritten
+        assert hook.find_module("test_foo") is not None
+        assert self.find_module_calls == ["conftest", "test_foo"]
+
+        # file does not match "python_files": early bailout
+        assert hook.find_module("bar") is None
+        assert self.find_module_calls == ["conftest", "test_foo"]
+
+        # file is an initial path (passed on the command-line): should be rewritten
+        assert hook.find_module("foobar") is not None
+        assert self.find_module_calls == ["conftest", "test_foo", "foobar"]
+
+    def test_pattern_contains_subdirectories(self, testdir, hook):
+        """If one of the python_files patterns contain subdirectories ("tests/**.py") we can't bailout early
+        because we need to match with the full path, which can only be found by calling imp.find_module.
+        """
+        p = testdir.makepyfile(
+            **{
+                "tests/file.py": """
+                        def test_simple_failure():
+                            assert 1 + 1 == 3
+                        """
+            }
+        )
+        testdir.syspathinsert(p.dirpath())
+        hook.fnpats[:] = ["tests/**.py"]
+        assert hook.find_module("file") is not None
+        assert self.find_module_calls == ["file"]