diff --git a/glean-core/python/glean/metrics/event.py b/glean-core/python/glean/metrics/event.py
index faa5c7601..7839144b0 100644
--- a/glean-core/python/glean/metrics/event.py
+++ b/glean-core/python/glean/metrics/event.py
@@ -74,7 +74,7 @@ class EventMetricType:
 
         self._inner.record(extra)
 
-    def test_get_value(self, ping_name: Optional[str] = None) -> List[RecordedEvent]:
+    def test_get_value(self, ping_name: Optional[str] = None) -> Optional[List[RecordedEvent]]:
         """
         Returns the stored value for testing purposes only.
 
diff --git a/glean-core/python/glean/metrics/string.py b/glean-core/python/glean/metrics/string.py
index 67dafe58f..a8bb30d69 100644
--- a/glean-core/python/glean/metrics/string.py
+++ b/glean-core/python/glean/metrics/string.py
@@ -40,7 +40,7 @@ class StringMetricType:
 
         self._inner.set(value)
 
-    def test_get_value(self, ping_name: Optional[str] = None) -> str:
+    def test_get_value(self, ping_name: Optional[str] = None) -> Optional[str]:
         return self._inner.test_get_value(ping_name)
 
     def test_get_num_recorded_errors(
diff --git a/glean-core/python/glean/metrics/timespan.py b/glean-core/python/glean/metrics/timespan.py
index 730bfbb30..712b80e4d 100644
--- a/glean-core/python/glean/metrics/timespan.py
+++ b/glean-core/python/glean/metrics/timespan.py
@@ -103,7 +103,7 @@ class TimespanMetricType:
         """
         self._inner.set_raw_nanos(elapsed_nanos)
 
-    def test_get_value(self, ping_name: Optional[str] = None) -> int:
+    def test_get_value(self, ping_name: Optional[str] = None) -> Optional[int]:
         """
         Returns the stored value for testing purposes only.
 
diff --git a/glean-core/python/glean/metrics/timing_distribution.py b/glean-core/python/glean/metrics/timing_distribution.py
index 4529cef8c..978953219 100644
--- a/glean-core/python/glean/metrics/timing_distribution.py
+++ b/glean-core/python/glean/metrics/timing_distribution.py
@@ -96,7 +96,9 @@ class TimingDistributionMetricType:
         """
         return self._TimingDistributionContextManager(self)
 
-    def test_get_value(self, ping_name: Optional[str] = None) -> DistributionData:
+    def test_get_value(
+        self, ping_name: Optional[str] = None
+    ) -> Optional[DistributionData]:
         """
         Returns the stored value for testing purposes only.
 
diff --git a/glean-core/python/glean/metrics/url.py b/glean-core/python/glean/metrics/url.py
index dac5e8132..03f85e704 100644
--- a/glean-core/python/glean/metrics/url.py
+++ b/glean-core/python/glean/metrics/url.py
@@ -41,7 +41,7 @@ class UrlMetricType:
 
         self._inner.set(value)
 
-    def test_get_value(self, ping_name: Optional[str] = None) -> str:
+    def test_get_value(self, ping_name: Optional[str] = None) -> Optional[str]:
         return self._inner.test_get_value(ping_name)
 
     def test_get_num_recorded_errors(