Seems like a exception message difference only. Might be fixed upstream in newer versions, I will check/report/fix.

Seems to be fixed in https://github.com/pytest-dev/pytest/commit/d9ac2efbcdee123f73edf1829c8bd6a91be3b6d2 (not yet released)

Backporting the patch, also to pytest4.

Fedora backport for pytest 6: https://src.fedoraproject.org/rpms/pytest/pull-request/18

Upstream backport for pytest 4: https://github.com/pytest-dev/pytest/pull/8054

Fedora backport for pytest 4: https://src.fedoraproject.org/rpms/python-pytest4/pull-request/2

There is a new failure now:

=================================== FAILURES ===================================
_____________________________ test_syspath_prepend _____________________________

mp = <_pytest.monkeypatch.MonkeyPatch object at 0x7f2164af4bb0>

    def test_syspath_prepend(mp: MonkeyPatch) -> None:
        old = list(sys.path)
>       mp.syspath_prepend("world")

testing/test_monkeypatch.py:252: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
../../BUILDROOT/pytest-6.0.2-1.fc34.x86_64/usr/lib/python3.10/site-packages/_pytest/monkeypatch.py:300: in syspath_prepend
    from pkg_resources import fixup_namespace_packages
/usr/lib/python3.10/site-packages/pkg_resources/__init__.py:73: in <module>
    from pkg_resources.extern import appdirs
<frozen importlib._bootstrap>:1026: in _find_and_load
    ???
<frozen importlib._bootstrap>:1005: in _find_and_load_unlocked
    ???
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

spec = ModuleSpec(name='pkg_resources.extern.appdirs', loader=<pkg_resources.extern.VendorImporter object at 0x7f2164a68d60>)

>   ???
E   ImportWarning: VendorImporter.exec_module() not found; falling back to load_module()

<frozen importlib._bootstrap>:681: ImportWarning
_______________________ test_syspath_prepend_double_undo _______________________

mp = <_pytest.monkeypatch.MonkeyPatch object at 0x7f2164a31040>

    def test_syspath_prepend_double_undo(mp: MonkeyPatch) -> None:
        old_syspath = sys.path[:]
        try:
>           mp.syspath_prepend("hello world")

testing/test_monkeypatch.py:265: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
../../BUILDROOT/pytest-6.0.2-1.fc34.x86_64/usr/lib/python3.10/site-packages/_pytest/monkeypatch.py:300: in syspath_prepend
    from pkg_resources import fixup_namespace_packages
/usr/lib/python3.10/site-packages/pkg_resources/__init__.py:73: in <module>
    from pkg_resources.extern import appdirs
<frozen importlib._bootstrap>:1026: in _find_and_load
    ???
<frozen importlib._bootstrap>:1005: in _find_and_load_unlocked
    ???
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

spec = ModuleSpec(name='pkg_resources.extern.appdirs', loader=<pkg_resources.extern.VendorImporter object at 0x7f2164a68d60>)

>   ???
E   ImportWarning: VendorImporter.exec_module() not found; falling back to load_module()

<frozen importlib._bootstrap>:681: ImportWarning
______________________ test_excinfo_no_python_sourcecode _______________________

tmpdir = local('/tmp/pytest-of-mockbuild/pytest-0/test_excinfo_no_python_sourcec0')

    def test_excinfo_no_python_sourcecode(tmpdir):
        # XXX: simplified locally testable version
        tmpdir.join("test.txt").write("{{ h()}}:")
    
        jinja2 = pytest.importorskip("jinja2")
        loader = jinja2.FileSystemLoader(str(tmpdir))
        env = jinja2.Environment(loader=loader)
        template = env.get_template("test.txt")
        excinfo = pytest.raises(ValueError, template.render, h=h)
        for item in excinfo.traceback:
            print(item)  # XXX: for some reason jinja.Template.render is printed in full
            item.source  # shouldn't fail
            if isinstance(item.path, py.path.local) and item.path.basename == "test.txt":
>               assert str(item.source) == "{{ h()}}:"
E               AssertionError: assert '' == '{{ h()}}:'
E                 - {{ h()}}:

testing/code/test_excinfo.py:382: AssertionError
----------------------------- Captured stdout call -----------------------------
  File '/builddir/build/BUILDROOT/pytest-6.0.2-1.fc34.x86_64/usr/lib/python3.10/site-packages/_pytest/python_api.py':706 in raises
  func(*args[1:], **kwargs)

  File '/usr/lib/python3.10/site-packages/jinja2/environment.py':1090 in render
  self.environment.handle_exception()

  File '/usr/lib/python3.10/site-packages/jinja2/environment.py':832 in handle_exception
  reraise(*rewrite_traceback_stack(source=source))

  File '/usr/lib/python3.10/site-packages/jinja2/_compat.py':28 in reraise
  raise value.with_traceback(tb)

  File '/tmp/pytest-of-mockbuild/pytest-0/test_excinfo_no_python_sourcec0/test.txt':-4 in top-level template code
  ???

_________ TestInvocationVariants.test_cmdline_python_namespace_package _________

self = <acceptance_test.TestInvocationVariants object at 0x7f214e9e9850>
testdir = <Testdir local('/tmp/pytest-of-mockbuild/pytest-0/test_cmdline_python_namespace_package0')>
monkeypatch = <_pytest.monkeypatch.MonkeyPatch object at 0x7f214ea007f0>

    def test_cmdline_python_namespace_package(self, testdir, monkeypatch):
        """
        test --pyargs option with namespace packages (#1567)
    
        Ref: https://packaging.python.org/guides/packaging-namespace-packages/
        """
        monkeypatch.delenv("PYTHONDONTWRITEBYTECODE", raising=False)
    
        search_path = []
        for dirname in "hello", "world":
            d = testdir.mkdir(dirname)
            search_path.append(d)
            ns = d.mkdir("ns_pkg")
            ns.join("__init__.py").write(
                "__import__('pkg_resources').declare_namespace(__name__)"
            )
            lib = ns.mkdir(dirname)
            lib.ensure("__init__.py")
            lib.join("test_{}.py".format(dirname)).write(
                "def test_{}(): pass\ndef test_other():pass".format(dirname)
            )
    
        # The structure of the test directory is now:
        # .
        # ├── hello
        # │   └── ns_pkg
        # │       ├── __init__.py
        # │       └── hello
        # │           ├── __init__.py
        # │           └── test_hello.py
        # └── world
        #     └── ns_pkg
        #         ├── __init__.py
        #         └── world
        #             ├── __init__.py
        #             └── test_world.py
    
        # NOTE: the different/reversed ordering is intentional here.
        monkeypatch.setenv("PYTHONPATH", prepend_pythonpath(*search_path))
        for p in search_path:
            monkeypatch.syspath_prepend(p)
    
        # mixed module and filenames:
        monkeypatch.chdir("world")
        result = testdir.runpytest("--pyargs", "-v", "ns_pkg.hello", "ns_pkg/world")
        assert result.ret == 0
>       result.stdout.fnmatch_lines(
            [
                "test_hello.py::test_hello*PASSED*",
                "test_hello.py::test_other*PASSED*",
                "ns_pkg/world/test_world.py::test_world*PASSED*",
                "ns_pkg/world/test_world.py::test_other*PASSED*",
                "*4 passed in*",
            ]
        )
E       Failed: nomatch: 'test_hello.py::test_hello*PASSED*'
E           and: '============================= test session starts =============================='
E           and: 'platform linux -- Python 3.10.0a3, pytest-6.0.2, py-1.9.0, pluggy-0.13.1 -- /usr/bin/python3'
E           and: 'cachedir: .pytest_cache'
E           and: 'rootdir: /tmp/pytest-of-mockbuild/pytest-0/test_cmdline_python_namespace_package0/world'
E           and: 'collecting ... collected 4 items'
E           and: ''
E       fnmatch: 'test_hello.py::test_hello*PASSED*'
E          with: 'test_hello.py::test_hello PASSED                                         [ 25%]'
E       fnmatch: 'test_hello.py::test_other*PASSED*'
E          with: 'test_hello.py::test_other PASSED                                         [ 50%]'
E       fnmatch: 'ns_pkg/world/test_world.py::test_world*PASSED*'
E          with: 'ns_pkg/world/test_world.py::test_world PASSED                            [ 75%]'
E       fnmatch: 'ns_pkg/world/test_world.py::test_other*PASSED*'
E          with: 'ns_pkg/world/test_world.py::test_other PASSED                            [100%]'
E       nomatch: '*4 passed in*'
E           and: ''
E           and: '=============================== warnings summary ==============================='
E           and: '<frozen importlib._bootstrap>:283'
E           and: '  <frozen importlib._bootstrap>:283: DeprecationWarning: the load_module() method is deprecated and slated for removal in Python 3.12; use exec_module() instead'
E           and: ''
E           and: '-- Docs: https://docs.pytest.org/en/stable/warnings.html'
E           and: '========================= 4 passed, 1 warning in 0.02s ========================='
E       remains unmatched: '*4 passed in*'

/builddir/build/BUILD/pytest-6.0.2/testing/acceptance_test.py:712: Failed
----------------------------- Captured stdout call -----------------------------
============================= test session starts ==============================
platform linux -- Python 3.10.0a3, pytest-6.0.2, py-1.9.0, pluggy-0.13.1 -- /usr/bin/python3
cachedir: .pytest_cache
rootdir: /tmp/pytest-of-mockbuild/pytest-0/test_cmdline_python_namespace_package0/world
collecting ... collected 4 items

test_hello.py::test_hello PASSED                                         [ 25%]
test_hello.py::test_other PASSED                                         [ 50%]
ns_pkg/world/test_world.py::test_world PASSED                            [ 75%]
ns_pkg/world/test_world.py::test_other PASSED                            [100%]

=============================== warnings summary ===============================
<frozen importlib._bootstrap>:283
  <frozen importlib._bootstrap>:283: DeprecationWarning: the load_module() method is deprecated and slated for removal in Python 3.12; use exec_module() instead

-- Docs: https://docs.pytest.org/en/stable/warnings.html
========================= 4 passed, 1 warning in 0.02s =========================
_________________ test_syspath_prepend_with_namespace_packages _________________

testdir = <Testdir local('/tmp/pytest-of-mockbuild/pytest-0/test_syspath_prepend_with_namespace_packages0')>
monkeypatch = <_pytest.monkeypatch.MonkeyPatch object at 0x7f212eded160>

    def test_syspath_prepend_with_namespace_packages(
        testdir: Testdir, monkeypatch: MonkeyPatch
    ) -> None:
        for dirname in "hello", "world":
            d = testdir.mkdir(dirname)
            ns = d.mkdir("ns_pkg")
            ns.join("__init__.py").write(
                "__import__('pkg_resources').declare_namespace(__name__)"
            )
            lib = ns.mkdir(dirname)
            lib.join("__init__.py").write("def check(): return %r" % dirname)
    
>       monkeypatch.syspath_prepend("hello")

/builddir/build/BUILD/pytest-6.0.2/testing/test_monkeypatch.py:427: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
/builddir/build/BUILDROOT/pytest-6.0.2-1.fc34.x86_64/usr/lib/python3.10/site-packages/_pytest/monkeypatch.py:307: in syspath_prepend
    fixup_namespace_packages(str(path))
/usr/lib/python3.10/site-packages/pkg_resources/__init__.py:2290: in fixup_namespace_packages
    subpath = _handle_ns(package, path_item)
/usr/lib/python3.10/site-packages/pkg_resources/__init__.py:2212: in _handle_ns
    loader.load_module(packageName)
<frozen importlib._bootstrap_external>:508: in _check_name_wrapper
    ???
<frozen importlib._bootstrap_external>:1012: in load_module
    ???
<frozen importlib._bootstrap_external>:837: in load_module
    ???
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <_frozen_importlib_external.SourceFileLoader object at 0x7f212eded400>
fullname = 'ns_pkg'

>   ???
E   DeprecationWarning: the load_module() method is deprecated and slated for removal in Python 3.12; use exec_module() instead

<frozen importlib._bootstrap>:283: DeprecationWarning
_________________ TestPDB.test_pdb_interaction_capturing_twice _________________

self = <test_debugging.TestPDB object at 0x7f2119db88e0>
testdir = <Testdir local('/tmp/pytest-of-mockbuild/pytest-0/test_pdb_interaction_capturing_twice0')>

    def test_pdb_interaction_capturing_twice(self, testdir):
        p1 = testdir.makepyfile(
            """
            import pytest
            def test_1():
                i = 0
                print("hello17")
                pytest.set_trace()
                x = 3
                print("hello18")
                pytest.set_trace()
                x = 4
                assert 0
        """
        )
        child = testdir.spawn_pytest(str(p1))
        child.expect(r"PDB set_trace \(IO-capturing turned off\)")
        child.expect("test_1")
        child.expect("x = 3")
        child.expect("Pdb")
        child.sendline("c")
        child.expect(r"PDB continue \(IO-capturing resumed\)")
        child.expect(r"PDB set_trace \(IO-capturing turned off\)")
>       child.expect("x = 4")

/builddir/build/BUILD/pytest-6.0.2/testing/test_debugging.py:545: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
/usr/lib/python3.10/site-packages/pexpect/spawnbase.py:343: in expect
    return self.expect_list(compiled_pattern_list,
/usr/lib/python3.10/site-packages/pexpect/spawnbase.py:372: in expect_list
    return exp.expect_loop(timeout)
/usr/lib/python3.10/site-packages/pexpect/expect.py:181: in expect_loop
    return self.timeout(e)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <pexpect.expect.Expecter object at 0x7f211a09f0d0>
err = TIMEOUT('Timeout exceeded.')

    def timeout(self, err=None):
        spawn = self.spawn
    
        spawn.before = spawn._before.getvalue()
        spawn.after = TIMEOUT
        index = self.searcher.timeout_index
        if index >= 0:
            spawn.match = TIMEOUT
            spawn.match_index = index
            return index
        else:
            spawn.match = None
            spawn.match_index = None
            msg = str(spawn)
            msg += '\nsearcher: %s' % self.searcher
            if err is not None:
                msg = str(err) + '\n' + msg
    
            exc = TIMEOUT(msg)
            exc.__cause__ = None    # in Python 3.x we can use "raise exc from None"
>           raise exc
E           pexpect.exceptions.TIMEOUT: Timeout exceeded.
E           <pexpect.pty_spawn.spawn object at 0x7f2119db8940>
E           command: /usr/bin/python3
E           args: ['/usr/bin/python3', '-mpytest', '--basetemp=/tmp/pytest-of-mockbuild/pytest-0/test_pdb_interaction_capturing_twice0/temp-pexpect', '/tmp/pytest-of-mockbuild/pytest-0/test_pdb_interaction_capturing_twice0/test_pdb_interaction_capturing_twice.py']
E           buffer (last 100 chars): b'n_capturing_twice0/test_pdb_interaction_capturing_twice.py(8)test_1()\r\n-> pytest.set_trace()\r\n(Pdb) '
E           before (last 100 chars): b'n_capturing_twice0/test_pdb_interaction_capturing_twice.py(8)test_1()\r\n-> pytest.set_trace()\r\n(Pdb) '
E           after: <class 'pexpect.exceptions.TIMEOUT'>
E           match: None
E           match_index: None
E           exitstatus: None
E           flag_eof: False
E           pid: 8768
E           child_fd: 20
E           closed: False
E           timeout: 10.0
E           delimiter: <class 'pexpect.exceptions.EOF'>
E           logfile: <_io.BufferedWriter name='/tmp/pytest-of-mockbuild/pytest-0/test_pdb_interaction_capturing_twice0/spawn.out'>
E           logfile_read: None
E           logfile_send: None
E           maxread: 2000
E           ignorecase: False
E           searchwindowsize: None
E           delaybeforesend: 0.05
E           delayafterclose: 0.1
E           delayafterterminate: 0.1
E           searcher: searcher_re:
E               0: re.compile(b'x = 4')

/usr/lib/python3.10/site-packages/pexpect/expect.py:144: TIMEOUT

There are new failures.

Looks like there are new failures. 

=================================== FAILURES ===================================
_____________________ TestPDB.test_pdb_interaction_doctest _____________________

>       assert "\r\n'i=0.'\r\n" in child.before.decode("utf8")
E       assert "\r\n'i=0.'\r\n" in ") 'i=%i.' % i\r\n\x1b[?2004l\r'i=0.'\r\n\x1b[?2004h("
E        +  where ") 'i=%i.' % i\r\n\x1b[?2004l\r'i=0.'\r\n\x1b[?2004h(" = <built-in method decode of bytes object at 0x7f4483068b70>('utf8')
E        +    where <built-in method decode of bytes object at 0x7f4483068b70> = b") 'i=%i.' % i\r\n\x1b[?2004l\r'i=0.'\r\n\x1b[?2004h(".decode
E        +      where b") 'i=%i.' % i\r\n\x1b[?2004l\r'i=0.'\r\n\x1b[?2004h(" = <pexpect.pty_spawn.spawn object at 0x7f4483095ca0>.before



___________________ TestPDB.test_pdb_with_injected_do_debug ____________________
>           raise exc
E           pexpect.exceptions.TIMEOUT: Timeout exceeded.
E           <pexpect.pty_spawn.spawn object at 0x7f448308ddc0>
E           command: /usr/bin/python3
E           args: ['/usr/bin/python3', '-mpytest', '--basetemp=/tmp/pytest-of-mockbuild/pytest-0/test_pdb_with_injected_do_debug0/temp-pexpect', '--pdbcls=mytest:CustomPdb', '/tmp/pytest-of-mockbuild/pytest-0/test_pdb_with_injected_do_debug0/mytest.py']
E           buffer (last 100 chars): b'-mockbuild/pytest-0/test_pdb_with_injected_do_debug0/mytest.py(34)test_1()\r\n-> x = 3\r\n\x1b[?2004h(Pdb) '
E           before (last 100 chars): b'-mockbuild/pytest-0/test_pdb_with_injected_do_debug0/mytest.py(34)test_1()\r\n-> x = 3\r\n\x1b[?2004h(Pdb) '
E           after: <class 'pexpect.exceptions.TIMEOUT'>
E           match: None
E           match_index: None
E           exitstatus: None
E           flag_eof: False
E           pid: 762
E           child_fd: 22
E           closed: False
E           timeout: 10.0
E           delimiter: <class 'pexpect.exceptions.EOF'>
E           logfile: <_io.BufferedWriter name='/tmp/pytest-of-mockbuild/pytest-0/test_pdb_with_injected_do_debug0/spawn.out'>
E           logfile_read: None
E           logfile_send: None
E           maxread: 2000
E           ignorecase: False
E           searchwindowsize: None
E           delaybeforesend: 0.05
E           delayafterclose: 0.1
E           delayafterterminate: 0.1
E           searcher: searcher_re:
E               0: re.compile(b'\\n\\(Pdb')

_______________ TestPDB.test_pdb_continue_with_recursive_debug[] _______________
>       assert "\r\nENTERING RECURSIVE DEBUGGER\r\n" in before
E       AssertionError: assert '\r\nENTERING RECURSIVE DEBUGGER\r\n' in '\r\n\x1b[?2004hdebug set_trace()\r\n\x1b[?2004l\rENTERING RECURSIVE DEBUGGER\r\n'

______________ TestPDB.test_pdb_continue_with_recursive_debug[-s] ______________

>       assert "\r\nENTERING RECURSIVE DEBUGGER\r\n" in before
E       AssertionError: assert '\r\nENTERING RECURSIVE DEBUGGER\r\n' in '\r\n\x1b[?2004hdebug set_trace()\r\n\x1b[?2004l\rENTERING RECURSIVE DEBUGGER\r\n'

________ TestPDB.test_pdb_continue_with_recursive_debug[-p no:capture] _________

>       assert "\r\nENTERING RECURSIVE DEBUGGER\r\n" in before
E       AssertionError: assert '\r\nENTERING RECURSIVE DEBUGGER\r\n' in '\r\n\x1b[?2004hdebug set_trace()\r\n\x1b[?2004l\rENTERING RECURSIVE DEBUGGER\r\n'

__________________ test_pdb_suspends_fixture_capturing[capfd] __________________

>       assert "\r\n42\r\n" in child.before.decode("utf8")
E       AssertionError: assert '\r\n42\r\n' in ') p 40 + 2\r\n\x1b[?2004l\r42\r\n\x1b[?2004h('
E        +  where ') p 40 + 2\r\n\x1b[?2004l\r42\r\n\x1b[?2004h(' = <built-in method decode of bytes object at 0x7f448313eb70>('utf8')
E        +    where <built-in method decode of bytes object at 0x7f448313eb70> = b') p 40 + 2\r\n\x1b[?2004l\r42\r\n\x1b[?2004h('.decode
E        +      where b') p 40 + 2\r\n\x1b[?2004l\r42\r\n\x1b[?2004h(' = <pexpect.pty_spawn.spawn object at 0x7f4482e61910>.before

_________________ test_pdb_suspends_fixture_capturing[capsys] __________________

>       assert "\r\n42\r\n" in child.before.decode("utf8")
E       AssertionError: assert '\r\n42\r\n' in ') p 40 + 2\r\n\x1b[?2004l\r42\r\n\x1b[?2004h('
E        +  where ') p 40 + 2\r\n\x1b[?2004l\r42\r\n\x1b[?2004h(' = <built-in method decode of bytes object at 0x7f4482fbb300>('utf8')
E        +    where <built-in method decode of bytes object at 0x7f4482fbb300> = b') p 40 + 2\r\n\x1b[?2004l\r42\r\n\x1b[?2004h('.decode
E        +      where b') p 40 + 2\r\n\x1b[?2004l\r42\r\n\x1b[?2004h(' = <pexpect.pty_spawn.spawn object at 0x7f4482fa1bb0>.before

=========================== short test summary info ============================
FAILED testing/test_debugging.py::TestPDB::test_pdb_interaction_doctest - ass...
FAILED testing/test_debugging.py::TestPDB::test_pdb_interaction_capturing_twice
FAILED testing/test_debugging.py::TestPDB::test_pdb_with_injected_do_debug - ...
FAILED testing/test_debugging.py::TestPDB::test_pdb_continue_with_recursive_debug[]
FAILED testing/test_debugging.py::TestPDB::test_pdb_continue_with_recursive_debug[-s]
FAILED testing/test_debugging.py::TestPDB::test_pdb_continue_with_recursive_debug[-p no:capture]
FAILED testing/test_debugging.py::test_pdb_suspends_fixture_capturing[capfd]
FAILED testing/test_debugging.py::test_pdb_suspends_fixture_capturing[capsys]

the escape sequences: https://github.com/pytest-dev/pytest/issues/8256

This bug appears to have been reported against 'rawhide' during the Fedora 34 development cycle.
Changing version to 34.

Appears to be solved: https://copr.fedorainfracloud.org/coprs/g/python/python3.10/package/pytest/