Create isSubDict test method (facebook#3147)

Summary:
Pull Request resolved: facebook#3147

Utility method for checking dicts have at least certain fields defined with certain values, where extra fields will not break functionality.

Breaking this out as an OSS change.

Reviewed By: ItsMrLin

Differential Revision: D66770059

fbshipit-source-id: 5e1bbaa69b1f597ef21540bd5c21ad158ef6c716

Author: Daniel Cohen

ax/utils/common/testutils.py

@@ -485,6 +485,33 @@ def assertDictsAlmostEqual(
             else:
                 self.assertEqual(a_field, b_field, msg=msg)
 
+    def assertIsSubDict(
+        self,
+        subdict: dict[str, Any],
+        superdict: dict[str, Any],
+        almost_equal: bool = False,
+        consider_nans_equal: bool = False,
+    ) -> None:
+        """Testing utility that checks that all keys and values of `subdict` are
+        contained in `dict`.
+
+        Args:
+            subdict: A smaller dictionary.
+            superdict: A larger dictionary which should contain all keys of subdict
+                and the same values as subdict for the corresponding keys.
+        """
+        intersection_dict = {k: superdict[k] for k in subdict}
+        if consider_nans_equal and not almost_equal:
+            raise ValueError(
+                "`consider_nans_equal` can only be used with `almost_equal`"
+            )
+        if almost_equal:
+            self.assertDictsAlmostEqual(
+                subdict, intersection_dict, consider_nans_equal=consider_nans_equal
+            )
+        else:
+            self.assertEqual(subdict, intersection_dict)
+
     @staticmethod
     @contextlib.contextmanager
     def silence_stderr() -> Generator[None, None, None]: