Making --debug more configurable for the pytest user (#8955)

Close #8954

Author: symonk

.gitignore

@@ -53,3 +53,6 @@ coverage.xml
 
 # generated by pip
 pip-wheel-metadata/
+
+# pytest debug logs generated via --debug
+pytestdebug.log

changelog/8954.feature.rst

@@ -0,0 +1 @@
+``--debug`` flag now accepts a :class:`str` file to route debug logs into, remains defaulted to `pytestdebug.log`.

src/_pytest/helpconfig.py

@@ -80,10 +80,14 @@ def pytest_addoption(parser: Parser) -> None:
     )
     group.addoption(
         "--debug",
-        action="store_true",
+        action="store",
+        nargs="?",
+        const="pytestdebug.log",
         dest="debug",
-        default=False,
-        help="store internal tracing debug information in 'pytestdebug.log'.",
+        metavar="DEBUG_FILE_NAME",
+        help="store internal tracing debug information in this log file.\n"
+        "This file is opened with 'w' and truncated as a result, care advised.\n"
+        "Defaults to 'pytestdebug.log'.",
     )
     group._addoption(
         "-o",
@@ -98,8 +102,10 @@ def pytest_addoption(parser: Parser) -> None:
 def pytest_cmdline_parse():
     outcome = yield
     config: Config = outcome.get_result()
+
     if config.option.debug:
-        path = os.path.abspath("pytestdebug.log")
+        # --debug | --debug <file.log> was provided.
+        path = config.option.debug
         debugfile = open(path, "w")
         debugfile.write(
             "versions pytest-%s, py-%s, "
@@ -114,11 +120,11 @@ def pytest_cmdline_parse():
         )
         config.trace.root.setwriter(debugfile.write)
         undo_tracing = config.pluginmanager.enable_tracing()
-        sys.stderr.write("writing pytestdebug information to %s\n" % path)
+        sys.stderr.write("writing pytest debug information to %s\n" % path)
 
         def unset_tracing() -> None:
             debugfile.close()
-            sys.stderr.write("wrote pytestdebug information to %s\n" % debugfile.name)
+            sys.stderr.write("wrote pytest debug information to %s\n" % debugfile.name)
             config.trace.root.setwriter(None)
             undo_tracing()
 

testing/test_config.py

@@ -2042,3 +2042,55 @@ def test_parse_warning_filter_failure(arg: str) -> None:
 
     with pytest.raises(warnings._OptionError):
         parse_warning_filter(arg, escape=True)
+
+
+class TestDebugOptions:
+    def test_without_debug_does_not_write_log(self, pytester: Pytester) -> None:
+        result = pytester.runpytest()
+        result.stderr.no_fnmatch_line(
+            "*writing pytest debug information to*pytestdebug.log"
+        )
+        result.stderr.no_fnmatch_line(
+            "*wrote pytest debug information to*pytestdebug.log"
+        )
+        assert not [f.name for f in pytester.path.glob("**/*.log")]
+
+    def test_with_only_debug_writes_pytestdebug_log(self, pytester: Pytester) -> None:
+        result = pytester.runpytest("--debug")
+        result.stderr.fnmatch_lines(
+            [
+                "*writing pytest debug information to*pytestdebug.log",
+                "*wrote pytest debug information to*pytestdebug.log",
+            ]
+        )
+        assert "pytestdebug.log" in [f.name for f in pytester.path.glob("**/*.log")]
+
+    def test_multiple_custom_debug_logs(self, pytester: Pytester) -> None:
+        result = pytester.runpytest("--debug", "bar.log")
+        result.stderr.fnmatch_lines(
+            [
+                "*writing pytest debug information to*bar.log",
+                "*wrote pytest debug information to*bar.log",
+            ]
+        )
+        result = pytester.runpytest("--debug", "foo.log")
+        result.stderr.fnmatch_lines(
+            [
+                "*writing pytest debug information to*foo.log",
+                "*wrote pytest debug information to*foo.log",
+            ]
+        )
+
+        assert {"bar.log", "foo.log"} == {
+            f.name for f in pytester.path.glob("**/*.log")
+        }
+
+    def test_debug_help(self, pytester: Pytester) -> None:
+        result = pytester.runpytest("-h")
+        result.stdout.fnmatch_lines(
+            [
+                "*store internal tracing debug information in this log*",
+                "*This file is opened with 'w' and truncated as a result*",
+                "*Defaults to 'pytestdebug.log'.",
+            ]
+        )