pygments themes are customizable

AUTHORS

@@ -106,6 +106,7 @@ Edson Tadeu M. Manoel
 Eduardo Schettino
 Eli Boyarski
 Elizaveta Shashkova
+Éloi Rivard
 Endre Galaczi
 Eric Hunsberger
 Eric Liu

changelog/7132.feature.rst

@@ -0,0 +1 @@
+Added two environment variables :envvar:`PYTEST_THEME` and :envvar:`PYTEST_THEME_MODE` to let the users customize the pygments theme used.

doc/en/reference/customize.rst

@@ -239,3 +239,11 @@ Builtin configuration file options
 ----------------------------------------------
 
 For the full list of options consult the :ref:`reference documentation <ini options ref>`.
+
+Syntax highlighting theme customization
+---------------------------------------
+
+The syntax highlighting themes used by pytest can be customized using two environment variables:
+
+- :envvar:`PYTEST_THEME` sets a `pygment style <https://pygments.org/docs/styles/>`_ to use.
+- :envvar:`PYTEST_THEME_MODE` sets this style to *light* or *dark*.

doc/en/reference/reference.rst

@@ -1075,6 +1075,14 @@ Contains comma-separated list of modules that should be loaded as plugins:
 
     export PYTEST_PLUGINS=mymodule.plugin,xdist
 
+.. envvar:: PYTEST_THEME
+
+Sets a `pygment style <https://pygments.org/docs/styles/>`_ to use for the code output.
+
+.. envvar:: PYTEST_THEME_MODE
+
+Sets the :envvar:`PYTEST_THEME` to be either *dark* or *light*.
+
 .. envvar:: PY_COLORS
 
 When set to ``1``, pytest will use color in terminal output.

src/_pytest/_io/terminalwriter.py

@@ -195,16 +195,39 @@ class TerminalWriter:
 
     def _highlight(self, source: str) -> str:
         """Highlight the given source code if we have markup support."""
+        from _pytest.config.exceptions import UsageError
+
         if not self.hasmarkup or not self.code_highlight:
             return source
         try:
             from pygments.formatters.terminal import TerminalFormatter
             from pygments.lexers.python import PythonLexer
             from pygments import highlight
+            import pygments.util
         except ImportError:
             return source
         else:
-            highlighted: str = highlight(
-                source, PythonLexer(), TerminalFormatter(bg="dark")
-            )
-            return highlighted
+            try:
+                highlighted: str = highlight(
+                    source,
+                    PythonLexer(),
+                    TerminalFormatter(
+                        bg=os.getenv("PYTEST_THEME_MODE", "dark"),
+                        style=os.getenv("PYTEST_THEME"),
+                    ),
+                )
+                return highlighted
+            except pygments.util.ClassNotFound:
+                raise UsageError(
+                    "PYTEST_THEME environment variable had an invalid value: '{}'. "
+                    "Only valid pygment styles are allowed.".format(
+                        os.getenv("PYTEST_THEME")
+                    )
+                )
+            except pygments.util.OptionError:
+                raise UsageError(
+                    "PYTEST_THEME_MODE environment variable had an invalid value: '{}'. "
+                    "The only allowed values are 'dark' and 'light'.".format(
+                        os.getenv("PYTEST_THEME_MODE")
+                    )
+                )

testing/test_terminal.py

@@ -2408,6 +2408,60 @@ class TestCodeHighlight:
             )
         )
 
+    def test_code_highlight_custom_theme(
+        self, pytester: Pytester, color_mapping, monkeypatch: MonkeyPatch
+    ) -> None:
+        pytester.makepyfile(
+            """
+            def test_foo():
+                assert 1 == 10
+        """
+        )
+        monkeypatch.setenv("PYTEST_THEME", "solarized-dark")
+        monkeypatch.setenv("PYTEST_THEME_MODE", "dark")
+        result = pytester.runpytest("--color=yes")
+        result.stdout.fnmatch_lines(
+            color_mapping.format_for_fnmatch(
+                [
+                    "    {kw}def{hl-reset} {function}test_foo{hl-reset}():",
+                    ">       {kw}assert{hl-reset} {number}1{hl-reset} == {number}10{hl-reset}",
+                    "{bold}{red}E       assert 1 == 10{reset}",
+                ]
+            )
+        )
+
+    def test_code_highlight_invalid_theme(
+        self, pytester: Pytester, color_mapping, monkeypatch: MonkeyPatch
+    ) -> None:
+        pytester.makepyfile(
+            """
+            def test_foo():
+                assert 1 == 10
+        """
+        )
+        monkeypatch.setenv("PYTEST_THEME", "invalid")
+        result = pytester.runpytest_subprocess("--color=yes")
+        result.stderr.fnmatch_lines(
+            "ERROR: PYTEST_THEME environment variable had an invalid value: 'invalid'. "
+            "Only valid pygment styles are allowed."
+        )
+
+    def test_code_highlight_invalid_theme_mode(
+        self, pytester: Pytester, color_mapping, monkeypatch: MonkeyPatch
+    ) -> None:
+        pytester.makepyfile(
+            """
+            def test_foo():
+                assert 1 == 10
+        """
+        )
+        monkeypatch.setenv("PYTEST_THEME_MODE", "invalid")
+        result = pytester.runpytest_subprocess("--color=yes")
+        result.stderr.fnmatch_lines(
+            "ERROR: PYTEST_THEME_MODE environment variable had an invalid value: 'invalid'. "
+            "The only allowed values are 'dark' and 'light'."
+        )
+
 
 def test_raw_skip_reason_skipped() -> None:
     report = SimpleNamespace()