Add tests to ensure that FieldValue has no cyclic references (#3869)

Author: schmidt-sebastian

packages/firestore/test/unit/api/field_value.test.ts

@@ -33,4 +33,12 @@ describe('FieldValue', () => {
     expect(FieldValue.arrayUnion('a')).to.be.an.instanceOf(FieldValue);
     expect(FieldValue.arrayRemove('a')).to.be.an.instanceOf(FieldValue);
   });
+
+  it('JSON.stringify() does not throw', () => {
+    JSON.stringify(FieldValue.delete());
+    JSON.stringify(FieldValue.serverTimestamp());
+    JSON.stringify(FieldValue.increment(1));
+    JSON.stringify(FieldValue.arrayUnion(2));
+    JSON.stringify(FieldValue.arrayRemove(3));
+  });
 });