fix(test-logging): don't store empty logs (ethereum#2547)

Author: felix314159

packages/testing/src/execution_testing/cli/tests/test_pytest_fill_command.py

@@ -209,6 +209,26 @@ def test_fill_no_html_option(
         run_fill(*fill_args)
         assert not default_html_path.exists()
 
+    def test_fill_pytest_help_does_not_create_empty_log_file(
+        self, pytester: Pytester
+    ) -> None:
+        """Help-mode startup should not leave behind an empty log file."""
+        log_dir = pytester.path / "logs"
+        pytester.copy_example(
+            name="src/execution_testing/cli/pytest_commands/pytest_ini_files/pytest-fill.ini"
+        )
+
+        result = pytester.runpytest(
+            "-c",
+            "pytest-fill.ini",
+            "--help",
+            "--log-to",
+            str(log_dir),
+        )
+
+        assert result.ret == pytest.ExitCode.OK
+        assert not list(log_dir.glob("*.log"))
+
     def test_generate_pre_alloc_groups_preserves_chain_id_for_valid_from(
         self,
         pytester: Pytester,

packages/testing/src/execution_testing/logging/logger.py

@@ -215,7 +215,9 @@ def configure_logging(
         log_path = Path(log_file)
         log_path.parent.mkdir(exist_ok=True, parents=True)
 
-        file_handler_instance = logging.FileHandler(log_path, mode="w")
+        file_handler_instance = logging.FileHandler(
+            log_path, mode="w", delay=True
+        )
         file_handler_instance.setFormatter(UTCFormatter(fmt=log_format))
         root_logger.addHandler(file_handler_instance)
 

packages/testing/src/execution_testing/logging/tests/test_logging.py

@@ -169,13 +169,14 @@ def test_configure_logging_with_file(self) -> None:
                 # Should return a file handler
                 assert isinstance(handler, logging.FileHandler)
 
-                # Should create the log file
-                assert log_file.exists()
+                # Delay file creation until the first record is emitted.
+                assert not log_file.exists()
 
                 # Log a message and check it appears in the file
                 logger = get_logger("test_config")
                 logger.info("Test log message")
 
+                assert log_file.exists()
                 with open(log_file, "r") as f:
                     log_content = f.read()
                     assert "Test log message" in log_content
@@ -258,12 +259,15 @@ def getoption(self, name: str) -> Any:
                 # Find the log file handler's file
                 log_file = Path(file_handlers[0].baseFilename)
 
-                # Check that the log file was created
-                assert log_file.exists()
-
                 # Verify the file is in the logs directory
                 assert log_file.parent.resolve() == log_dir.resolve()
 
+                # Delay file creation until the first record is emitted.
+                assert not log_file.exists()
+
+                get_logger("test_pytest_configure").info("Test log message")
+                assert log_file.exists()
+
                 # Clean up the test log file
                 log_file.unlink()