Fix cloudwatch list metrics localstack #5000 (#4732)

moto/cloudwatch/models.py

@@ -220,9 +220,14 @@ class MetricDatum(BaseModel):
             return False
 
         for metric in already_present_metrics or []:
-            if self.dimensions and are_dimensions_same(
-                metric.dimensions, self.dimensions
-            ):
+            if (
+                (
+                    self.dimensions
+                    and are_dimensions_same(metric.dimensions, self.dimensions)
+                )
+                and self.name == metric.name
+                and self.namespace == metric.namespace
+            ):  # should be considered as already present only when name, namespace and dimensions all three are same
                 return False
 
         if dimensions and any(

tests/test_cloudwatch/test_cloudwatch_boto3.py

@@ -400,6 +400,53 @@ def test_list_metrics_without_value():
     results[0]["Dimensions"].should.equal([{"Name": "D1", "Value": "V1"}])
 
 
+@mock_cloudwatch
+def test_list_metrics_with_same_dimensions_different_metric_name():
+    cloudwatch = boto3.client("cloudwatch", "eu-west-1")
+
+    # create metrics with same namespace and dimensions but different metric names
+    cloudwatch.put_metric_data(
+        Namespace="unique/",
+        MetricData=[
+            {
+                "MetricName": "metric1",
+                "Dimensions": [{"Name": "D1", "Value": "V1"}],
+                "Unit": "Seconds",
+            }
+        ],
+    )
+
+    cloudwatch.put_metric_data(
+        Namespace="unique/",
+        MetricData=[
+            {
+                "MetricName": "metric2",
+                "Dimensions": [{"Name": "D1", "Value": "V1"}],
+                "Unit": "Seconds",
+            }
+        ],
+    )
+
+    results = cloudwatch.list_metrics()["Metrics"]
+    results.should.have.length_of(2)
+
+    # duplicating existing metric
+    cloudwatch.put_metric_data(
+        Namespace="unique/",
+        MetricData=[
+            {
+                "MetricName": "metric1",
+                "Dimensions": [{"Name": "D1", "Value": "V1"}],
+                "Unit": "Seconds",
+            }
+        ],
+    )
+
+    # asserting only unique values are returned
+    results = cloudwatch.list_metrics()["Metrics"]
+    results.should.have.length_of(2)
+
+
 def create_metrics(cloudwatch, namespace, metrics=5, data_points=5):
     for i in range(0, metrics):
         metric_name = "metric" + str(i)