tests(metrics): fix tests when warnings are disabled

Changes:
- run 'make format'
- set 'warnings.simplefilter(default)'

closes #993

Author: Michael Brewer

Diff for: tests/functional/test_metrics.py

@@ -496,7 +496,8 @@ def lambda_handler(evt, context):
     # THEN ColdStart metric and function_name and service dimension should be logged
     assert output["ColdStart"] == [1.0]
     assert output["function_name"] == "example_fn"
-    assert output['service'] == service
+    assert output["service"] == service
+
 
 def test_log_metrics_capture_cold_start_metric_no_service(capsys, namespace):
     # GIVEN Metrics is initialized without service
@@ -515,7 +516,7 @@ def lambda_handler(evt, context):
     # THEN ColdStart metric and function_name dimension should be logged
     assert output["ColdStart"] == [1.0]
     assert output["function_name"] == "example_fn"
-    assert output.get('service') is None
+    assert output.get("service") is None
 
 
 def test_emit_cold_start_metric_only_once(capsys, namespace, service, metric):
@@ -551,6 +552,7 @@ def lambda_handler(evt, context):
 
     # THEN it should raise a warning instead of throwing an exception
     with warnings.catch_warnings(record=True) as w:
+        warnings.simplefilter("default")
         lambda_handler({}, {})
         assert len(w) == 1
         assert str(w[-1].message) == "No metrics to publish, skipping"