Fix fail in test_repo_trace if trace is disabled

If env has REPO_TRACE 0, then the test produces:
FileNotFoundError: No such file or directory: TRACE_FILE_from_test'
because it assumes trace is always enabled.

Improve by enabling trace for this test class.

Also modify the repo_trace.SetTrace API to take an optional
True/False if needed, still defaults to True though.

Change-Id: I2bb4632eb45ee529fc1785833e0bafd9c36f0875
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/445541
Commit-Queue: Fredrik de Groot <fredrik.de.groot@haleytek.com>
Reviewed-by: Mike Frysinger <vapier@google.com>
Reviewed-by: Brian Gan <brgan@google.com>
Tested-by: Fredrik de Groot <fredrik.de.groot@haleytek.com>

repo_trace.py

@@ -57,10 +57,10 @@ def SetTraceToStderr():
     _TRACE_TO_STDERR = True
 
 
-def SetTrace():
-    """Enables tracing."""
+def SetTrace(value: bool = True) -> None:
+    """Enables by default, or disables tracing."""
     global _TRACE
-    _TRACE = True
+    _TRACE = value
 
 
 def _SetTraceFile(quiet):

tests/conftest.py

@@ -26,6 +26,7 @@ import repo_trace
 @pytest.fixture(autouse=True)
 def disable_repo_trace(tmp_path):
     """Set an environment marker to relax certain strict checks for test code."""  # noqa: E501
+    repo_trace.SetTrace(False)
     repo_trace._TRACE_FILE = str(tmp_path / "TRACE_FILE_from_test")
 
 

tests/test_repo_trace.py

@@ -25,6 +25,9 @@ def test_trace_max_size_enforced(monkeypatch: pytest.MonkeyPatch) -> None:
     """Check Trace behavior."""
     content = "git chicken"
 
+    # Enable trace for the test, in case users have it disabled.
+    monkeypatch.setattr(repo_trace, "_TRACE", True)
+
     with repo_trace.Trace(content, first_trace=True):
         pass
     first_trace_size = os.path.getsize(repo_trace._TRACE_FILE)