test: ignore color in tracebacks

Python 3.13 adds color escape sequences to tracebacks.  GitHub Actions
sets FORCE_COLOR=1, so they appear in color there, but not locally.  We
don't care about that difference, so strip the escape sequences.

tests/helpers.py

@@ -397,3 +397,8 @@ def __init__(self, options: Iterable[str]) -> None:
     def get_output(self) -> str:
         """Get the output text from the `DebugControl`."""
         return self.io.getvalue()
+
+
+def without_color(text: str) -> str:
+    """Remove ANSI color-setting escape sequences."""
+    return re.sub(r"\033\[[\d;]+m", "", text)

tests/test_execfile.py

@@ -23,6 +23,7 @@
 from coverage.files import python_reported_file
 
 from tests.coveragetest import CoverageTest, TESTS_DIR, UsingModulesMixin
+from tests.helpers import without_color
 
 TRY_EXECFILE = os.path.join(TESTS_DIR, "modules/process_test/try_execfile.py")
 
@@ -188,7 +189,7 @@ def excepthook(*args):
             run_python_file(["excepthook_throw.py"])
         # The _ExceptionDuringRun exception has the RuntimeError as its argument.
         assert exc_info.value.args[1].args[0] == "Error Outside"
-        stderr = self.stderr()
+        stderr = without_color(self.stderr())
         assert "in excepthook\n" in stderr
         assert "Error in sys.excepthook:\n" in stderr
         assert "RuntimeError: Error Inside" in stderr

tests/test_process.py

@@ -27,7 +27,7 @@
 
 from tests import testenv
 from tests.coveragetest import CoverageTest, TESTS_DIR
-from tests.helpers import re_line, re_lines, re_lines_text
+from tests.helpers import re_line, re_lines, re_lines_text, without_color
 
 
 class ProcessTest(CoverageTest):
@@ -318,6 +318,7 @@ def f2():
         assert out == out2
 
         # But also make sure that the output is what we expect.
+        out = without_color(out)
         path = python_reported_file('throw.py')
         msg = f'File "{re.escape(path)}", line 8, in f2'
         assert re.search(msg, out)
@@ -969,8 +970,11 @@ def excepthook(*args):
         py_st, py_out = self.run_command_status("python excepthook_throw.py")
         assert cov_st == py_st
         assert cov_st == 1
-        assert "in excepthook" in py_out
-        assert cov_out == py_out
+        assert "in excepthook" in without_color(py_out)
+        # Don't know why: the Python output shows "Error in sys.excepthook" and
+        # "Original exception" in color.  The coverage output has the first in
+        # color and "Original" without color? Strip all the color.
+        assert without_color(cov_out) == without_color(py_out)
 
 
 class AliasedCommandTest(CoverageTest):
@@ -1177,6 +1181,7 @@ def test_removing_directory(self) -> None:
     def test_removing_directory_with_error(self) -> None:
         self.make_file("bug806.py", self.BUG_806)
         out = self.run_command("coverage run bug806.py")
+        out = without_color(out)
         path = python_reported_file('bug806.py')
         # Python 3.11 adds an extra line to the traceback.
         # Check that the lines we expect are there.

tests/test_testing.py

@@ -24,7 +24,7 @@
 from tests.helpers import (
     CheckUniqueFilenames, FailingProxy,
     arcs_to_arcz_repr, arcz_to_arcs, assert_count_equal, assert_coverage_warnings,
-    re_lines, re_lines_text, re_line,
+    re_lines, re_lines_text, re_line, without_color,
 )
 
 
@@ -472,3 +472,15 @@ def subtract(self, a, b):               # type: ignore[no-untyped-def]
         proxy.add(3, 4)
     # then add starts working
     assert proxy.add(5, 6) == 11
+
+
+@pytest.mark.parametrize("text, result", [
+    ("", ""),
+    ("Nothing to see here", "Nothing to see here"),
+    ("Oh no! \x1b[1;35mRuntimeError\x1b[0m. Fix it.", "Oh no! RuntimeError. Fix it."),
+    ("Fancy: \x1b[48;5;95mBkgd\x1b[38;2;100;200;25mRGB\x1b[0m", "Fancy: BkgdRGB"),
+    # Other escape sequences are unaffected.
+    ("X\x1b[2J\x1b[1mBold\x1b[22m\x1b[=3hZ", "X\x1b[2JBold\x1b[=3hZ"),
+])
+def test_without_color(text: str, result: str) -> None:
+    assert without_color(text) == result