Show diff to closest metric match

datadog_checks_base/changelog.d/18975.added

@@ -0,0 +1 @@
+Show diff to closest metric match when metric test fails

datadog_checks_base/datadog_checks/base/stubs/similar.py

@@ -9,6 +9,10 @@
 MAX_SIMILAR_TO_DISPLAY = 15
 
 
+def tags_list_to_dict(tags):
+    return {tag.split(':', 1)[0]: (tag.split(':', 1)[1] if ":" in tag else '') for tag in tags}
+
+
 def build_similar_elements_msg(expected, submitted_elements):
     """
     Return formatted similar elements (metrics, service checks) received compared to submitted elements
@@ -22,9 +26,34 @@ def build_similar_elements_msg(expected, submitted_elements):
             metric_stub.tags.sort()
         similar_metrics_to_print.append("{:.2f}    {}".format(score, metric_stub))
 
+    closest_diff = []
+    if len(similar_metrics) > 0:
+        [_, closest] = similar_metrics[0]
+        closest_dict = closest._asdict()
+        expected_dict = expected._asdict()
+        for key in closest_dict:
+            expected_value = expected_dict[key]
+            closest_value = closest_dict[key]
+
+            if expected_value is not None and expected_value != closest_value:
+                if key == "tags":
+                    expected_tags_dict = tags_list_to_dict(expected_value)
+                    closest_tags_dict = tags_list_to_dict(closest_value)
+                    for tag in expected_tags_dict:
+                        if closest_tags_dict[tag] != expected_tags_dict[tag]:
+                            closest_diff.append(
+                                f"        Expected tag {tag}:{expected_tags_dict[tag]}\n"
+                                + f"        Found {tag}:{closest_tags_dict[tag]}"
+                            )
+                else:
+                    closest_diff.append(f"        Expected {key}: {expected_value}\n        Found {closest_value}")
+
     return (
         "Expected:\n"
         + "        {}\n".format(expected)
+        + "Difference to closest:\n"
+        + "\n".join(closest_diff)
+        + "\n\n"
         + "Similar submitted:\n"
         + "Score   Most similar\n"
         + "\n".join(similar_metrics_to_print)

datadog_checks_base/tests/stubs/test_aggregator_similar.py

@@ -24,6 +24,10 @@ def test_build_similar_elements_msg(self, aggregator):
         expected_msg = '''
     Expected:
         MetricStub(name='test.similar_metric', type=None, value=None, tags=None, hostname=None, device=None, flush_first_value=None)
+Difference to closest:
+        Expected name: test.similar_metric
+        Found test.most_similar_metric
+
 Similar submitted:
 Score   Most similar
 0.88    MetricStub(name='test.most_similar_metric', type=0, value=0.0, tags=[], hostname='', device=None, flush_first_value=False)