diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 2a7da8136..e9a2f525d 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -54,6 +54,7 @@ jobs:
             python: "3.5"
             os: windows-latest
             tox_env: "py35-xdist"
+            use_coverage: true
           - name: "windows-py36"
             python: "3.6"
             os: windows-latest
@@ -70,6 +71,7 @@ jobs:
             python: "3.8"
             os: windows-latest
             tox_env: "py38"
+            use_coverage: true
 
           - name: "ubuntu-py35"
             python: "3.5"
@@ -83,6 +85,7 @@ jobs:
             python: "3.7"
             os: ubuntu-latest
             tox_env: "py37-lsof-numpy-oldattrs-pexpect-twisted"
+            use_coverage: true
           - name: "ubuntu-py37-pluggy"
             python: "3.7"
             os: ubuntu-latest
@@ -91,8 +94,6 @@ jobs:
             python: "3.7"
             os: ubuntu-latest
             tox_env: "py37-freeze"
-            # coverage does not apply for freeze test, skip it
-            skip_coverage: true
           - name: "ubuntu-py38"
             python: "3.8"
             os: ubuntu-latest
@@ -101,8 +102,6 @@ jobs:
             python: "pypy3"
             os: ubuntu-latest
             tox_env: "pypy3-xdist"
-            # coverage too slow with pypy3, skip it
-            skip_coverage: true
 
           - name: "macos-py37"
             python: "3.7"
@@ -112,21 +111,21 @@ jobs:
             python: "3.8"
             os: macos-latest
             tox_env: "py38-xdist"
+            use_coverage: true
 
           - name: "linting"
             python: "3.7"
             os: ubuntu-latest
             tox_env: "linting"
-            skip_coverage: true
           - name: "docs"
             python: "3.7"
             os: ubuntu-latest
             tox_env: "docs"
-            skip_coverage: true
           - name: "doctesting"
             python: "3.7"
             os: ubuntu-latest
             tox_env: "doctesting"
+            use_coverage: true
 
     steps:
     - uses: actions/checkout@v1
@@ -140,11 +139,11 @@ jobs:
         pip install tox coverage
 
     - name: Test without coverage
-      if: "matrix.skip_coverage"
+      if: "! matrix.use_coverage"
       run: "tox -e ${{ matrix.tox_env }}"
 
     - name: Test with coverage
-      if: "! matrix.skip_coverage"
+      if: "matrix.use_coverage"
       env:
         _PYTEST_TOX_COVERAGE_RUN: "coverage run -m"
         COVERAGE_PROCESS_START: ".coveragerc"
@@ -152,12 +151,12 @@ jobs:
       run: "tox -e ${{ matrix.tox_env }}"
 
     - name: Prepare coverage token
-      if: (!matrix.skip_coverage && ( github.repository == 'pytest-dev/pytest' || github.event_name == 'pull_request' ))
+      if: (matrix.use_coverage && ( github.repository == 'pytest-dev/pytest' || github.event_name == 'pull_request' ))
       run: |
         python scripts/append_codecov_token.py
 
     - name: Report coverage
-      if: (!matrix.skip_coverage)
+      if: (matrix.use_coverage)
       env:
         CODECOV_NAME: ${{ matrix.name }}
       run: bash scripts/report-coverage.sh -F GHA,${{ runner.os }}
diff --git a/AUTHORS b/AUTHORS
index 5eea42ea2..bd4c1fe5b 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -114,6 +114,7 @@ Guido Wesdorp
 Guoqiang Zhang
 Harald Armin Massa
 Henk-Jaap Wagenaar
+Holger Kohr
 Hugo van Kemenade
 Hui Wang (coldnight)
 Ian Bicking
diff --git a/changelog/6497.bugfix.rst b/changelog/6497.bugfix.rst
new file mode 100644
index 000000000..66d436abd
--- /dev/null
+++ b/changelog/6497.bugfix.rst
@@ -0,0 +1,4 @@
+Fix bug in the comparison of request key with cached key in fixture.
+
+A construct ``if key == cached_key:`` can fail either because ``==`` is explicitly disallowed, or for, e.g., NumPy arrays, where the result of ``a == b`` cannot generally be converted to `bool`.
+The implemented fix replaces `==` with ``is``.
diff --git a/src/_pytest/_code/code.py b/src/_pytest/_code/code.py
index 4cb373cc4..09245d84d 100644
--- a/src/_pytest/_code/code.py
+++ b/src/_pytest/_code/code.py
@@ -77,12 +77,11 @@ class Code:
             # maybe don't try this checking
             if not p.check():
                 raise OSError("py.path check failed.")
+            return p
         except OSError:
             # XXX maybe try harder like the weird logic
             # in the standard lib [linecache.updatecache] does?
-            p = self.raw.co_filename
-
-        return p
+            return self.raw.co_filename
 
     @property
     def fullsource(self) -> Optional["Source"]:
diff --git a/src/_pytest/fixtures.py b/src/_pytest/fixtures.py
index 9e60d56ce..08486fbff 100644
--- a/src/_pytest/fixtures.py
+++ b/src/_pytest/fixtures.py
@@ -548,8 +548,9 @@ class FixtureRequest:
                 frameinfo = inspect.getframeinfo(frame[0])
                 source_path = py.path.local(frameinfo.filename)
                 source_lineno = frameinfo.lineno
-                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 = (
@@ -896,7 +897,9 @@ class FixtureDef:
         cached_result = getattr(self, "cached_result", None)
         if cached_result is not None:
             result, cache_key, err = cached_result
-            if my_cache_key == cache_key:
+            # note: comparison with `==` can fail (or be expensive) for e.g.
+            # numpy arrays (#6497)
+            if my_cache_key is cache_key:
                 if err is not None:
                     _, val, tb = err
                     raise val.with_traceback(tb)
diff --git a/src/_pytest/monkeypatch.py b/src/_pytest/monkeypatch.py
index 090bf61d6..8aec7b818 100644
--- a/src/_pytest/monkeypatch.py
+++ b/src/_pytest/monkeypatch.py
@@ -4,6 +4,7 @@ import re
 import sys
 import warnings
 from contextlib import contextmanager
+from typing import Generator
 
 import pytest
 from _pytest.fixtures import fixture
@@ -108,7 +109,7 @@ class MonkeyPatch:
         self._savesyspath = None
 
     @contextmanager
-    def context(self):
+    def context(self) -> Generator["MonkeyPatch", None, None]:
         """
         Context manager that returns a new :class:`MonkeyPatch` object which
         undoes any patching done inside the ``with`` block upon exit:
diff --git a/src/_pytest/python_api.py b/src/_pytest/python_api.py
index 5e5eddc5b..24145016c 100644
--- a/src/_pytest/python_api.py
+++ b/src/_pytest/python_api.py
@@ -685,7 +685,7 @@ def raises(  # noqa: F811
     """
     __tracebackhide__ = True
     for exc in filterfalse(
-        inspect.isclass, always_iterable(expected_exception, BASE_TYPE)
+        inspect.isclass, always_iterable(expected_exception, BASE_TYPE)  # type: ignore[arg-type]  # noqa: F821
     ):
         msg = "exceptions must be derived from BaseException, not %s"
         raise TypeError(msg % type(exc))
diff --git a/testing/python/fixtures.py b/testing/python/fixtures.py
index 8cfaae50d..bfbe35951 100644
--- a/testing/python/fixtures.py
+++ b/testing/python/fixtures.py
@@ -1102,6 +1102,38 @@ class TestFixtureUsages:
             "*Fixture 'badscope' from test_invalid_scope.py got an unexpected scope value 'functions'"
         )
 
+    @pytest.mark.parametrize("scope", ["function", "session"])
+    def test_parameters_without_eq_semantics(self, scope, testdir):
+        testdir.makepyfile(
+            """
+            class NoEq1:  # fails on `a == b` statement
+                def __eq__(self, _):
+                    raise RuntimeError
+
+            class NoEq2:  # fails on `if a == b:` statement
+                def __eq__(self, _):
+                    class NoBool:
+                        def __bool__(self):
+                            raise RuntimeError
+                    return NoBool()
+
+            import pytest
+            @pytest.fixture(params=[NoEq1(), NoEq2()], scope={scope!r})
+            def no_eq(request):
+                return request.param
+
+            def test1(no_eq):
+                pass
+
+            def test2(no_eq):
+                pass
+        """.format(
+                scope=scope
+            )
+        )
+        result = testdir.runpytest()
+        result.stdout.fnmatch_lines(["*4 passed*"])
+
     def test_funcarg_parametrized_and_used_twice(self, testdir):
         testdir.makepyfile(
             """
@@ -3662,13 +3694,30 @@ 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(
diff --git a/testing/test_pytester.py b/testing/test_pytester.py
index ad951fdf5..d9230f90b 100644
--- a/testing/test_pytester.py
+++ b/testing/test_pytester.py
@@ -704,3 +704,13 @@ def test_testdir_outcomes_with_multiple_errors(testdir):
     result.assert_outcomes(error=2)
 
     assert result.parseoutcomes() == {"error": 2}
+
+
+def test_makefile_joins_absolute_path(testdir: Testdir) -> None:
+    absfile = testdir.tmpdir / "absfile"
+    if sys.platform == "win32":
+        with pytest.raises(OSError):
+            testdir.makepyfile(**{str(absfile): ""})
+    else:
+        p1 = testdir.makepyfile(**{str(absfile): ""})
+        assert str(p1) == (testdir.tmpdir / absfile) + ".py"