tests: cover absolute path handling in _compute_fixture_value

src/_pytest/fixtures.py

@@ -550,8 +550,9 @@ class FixtureRequest:
                 source_path = frameinfo.filename
                 source_lineno = frameinfo.lineno
                 source_path = py.path.local(source_path)
-                if source_path.relto(funcitem.config.rootdir):
-                    source_path_str = source_path.relto(funcitem.config.rootdir)
+                rel_source_path = source_path.relto(funcitem.config.rootdir)
+                if rel_source_path:
+                    source_path_str = rel_source_path
                 else:
                     source_path_str = str(source_path)
                 msg = (

testing/python/fixtures.py

@@ -3662,13 +3662,30 @@ class TestParameterizedSubRequest:
                 "    test_foos.py::test_foo",
                 "",
                 "Requested fixture 'fix_with_param' defined in:",
-                "*fix.py:4",
+                "{}:4".format(fixfile),
                 "Requested here:",
                 "test_foos.py:4",
                 "*1 failed*",
             ]
         )
 
+        # With non-overlapping rootdir, passing tests_dir.
+        rootdir = testdir.mkdir("rootdir")
+        rootdir.chdir()
+        result = testdir.runpytest("--rootdir", rootdir, tests_dir)
+        result.stdout.fnmatch_lines(
+            [
+                "The requested fixture has no parameter defined for test:",
+                "    test_foos.py::test_foo",
+                "",
+                "Requested fixture 'fix_with_param' defined in:",
+                "{}:4".format(fixfile),
+                "Requested here:",
+                "{}:4".format(testfile),
+                "*1 failed*",
+            ]
+        )
+
 
 def test_pytest_fixture_setup_and_post_finalizer_hook(testdir):
     testdir.makeconftest(