Resolve symlinks for args

This fixes running `pytest tests/test_foo.py::test_bar`, where `tests`
is a symlink to `project/app/tests`: previously
`project/app/conftest.py` would be ignored for fixtures then.

changelog/4108.bugfix.rst

@@ -0,0 +1 @@
+Resolve symbolic links for args.

src/_pytest/fixtures.py

@@ -1172,7 +1172,7 @@ def getfixtureinfo(self, node, func, cls, funcargs=True):
     def pytest_plugin_registered(self, plugin):
         nodeid = None
         try:
-            p = py.path.local(plugin.__file__)
+            p = py.path.local(plugin.__file__).realpath()
         except AttributeError:
             pass
         else:

src/_pytest/main.py

@@ -487,7 +487,7 @@ def _collect(self, arg):
         from _pytest.python import Package
 
         names = self._parsearg(arg)
-        argpath = names.pop(0)
+        argpath = names.pop(0).realpath()
         paths = []
 
         root = self

testing/acceptance_test.py

@@ -733,13 +733,14 @@ def join_pythonpath(*dirs):
             monkeypatch.syspath_prepend(p)
 
         # module picked up in symlink-ed directory:
+        # It picks up local/lib/foo/bar (symlink) via sys.path.
         result = testdir.runpytest("--pyargs", "-v", "foo.bar")
         testdir.chdir()
         assert result.ret == 0
         result.stdout.fnmatch_lines(
             [
-                "*lib/foo/bar/test_bar.py::test_bar*PASSED*",
-                "*lib/foo/bar/test_bar.py::test_other*PASSED*",
+                "lib/foo/bar/test_bar.py::test_bar <- local/lib/foo/bar/test_bar.py PASSED*",
+                "lib/foo/bar/test_bar.py::test_other <- local/lib/foo/bar/test_bar.py PASSED*",
                 "*2 passed*",
             ]
         )

testing/test_conftest.py

@@ -4,7 +4,7 @@
 import py
 import pytest
 from _pytest.config import PytestPluginManager
-from _pytest.main import EXIT_NOTESTSCOLLECTED, EXIT_USAGEERROR
+from _pytest.main import EXIT_NOTESTSCOLLECTED, EXIT_OK, EXIT_USAGEERROR
 
 
 @pytest.fixture(scope="module", params=["global", "inpackage"])
@@ -186,6 +186,48 @@ def pytest_addoption(parser):
     assert "warning: could not load initial" not in result.stdout.str()
 
 
+@pytest.mark.skipif(
+    not hasattr(py.path.local, "mksymlinkto"),
+    reason="symlink not available on this platform",
+)
+def test_conftest_symlink(testdir):
+    """Ensure that conftest.py is used for resolved symlinks."""
+    realtests = testdir.tmpdir.mkdir("real").mkdir("app").mkdir("tests")
+    testdir.tmpdir.join("symlinktests").mksymlinkto(realtests)
+    testdir.makepyfile(
+        **{
+            "real/app/tests/test_foo.py": "def test1(fixture): pass",
+            "real/conftest.py": textwrap.dedent(
+                """
+                import pytest
+
+                print("conftest_loaded")
+
+                @pytest.fixture
+                def fixture():
+                    print("fixture_used")
+                """
+            ),
+        }
+    )
+    result = testdir.runpytest("-vs", "symlinktests")
+    result.stdout.fnmatch_lines([
+        "*conftest_loaded*",
+        "real/app/tests/test_foo.py::test1 fixture_used",
+        "PASSED",
+    ])
+    assert result.ret == EXIT_OK
+
+    realtests.ensure("__init__.py")
+    result = testdir.runpytest("-vs", "symlinktests/test_foo.py::test1")
+    result.stdout.fnmatch_lines([
+        "*conftest_loaded*",
+        "real/app/tests/test_foo.py::test1 fixture_used",
+        "PASSED",
+    ])
+    assert result.ret == EXIT_OK
+
+
 def test_no_conftest(testdir):
     testdir.makeconftest("assert 0")
     result = testdir.runpytest("--noconftest")