Fix suspenseCallback type warning, add a test (#16194)

packages/react-reconciler/src/ReactFiberCommitWork.js

@@ -1330,7 +1330,9 @@ function commitSuspenseComponent(finishedWork: Fiber) {
         suspenseCallback(new Set(thenables));
       }
     } else if (__DEV__) {
-      warning(false, 'Unexpected type for suspenseCallback.');
+      if (suspenseCallback !== undefined) {
+        warning(false, 'Unexpected type for suspenseCallback.');
+      }
     }
   }
 }

packages/react-reconciler/src/__tests__/ReactSuspenseCallback-test.internal.js

@@ -50,6 +50,30 @@ describe('ReactSuspense', () => {
     return {promise, resolveRef, PromiseComp};
   }
 
+  it('check type', () => {
+    const {PromiseComp} = createThenable();
+
+    const elementBadType = (
+      <React.Suspense suspenseCallback={1} fallback={'Waiting'}>
+        <PromiseComp />
+      </React.Suspense>
+    );
+
+    ReactNoop.render(elementBadType);
+    expect(() => Scheduler.unstable_flushAll()).toWarnDev([
+      'Warning: Unexpected type for suspenseCallback.',
+    ]);
+
+    const elementMissingCallback = (
+      <React.Suspense fallback={'Waiting'}>
+        <PromiseComp />
+      </React.Suspense>
+    );
+
+    ReactNoop.render(elementMissingCallback);
+    expect(() => Scheduler.unstable_flushAll()).toWarnDev([]);
+  });
+
   it('1 then 0 suspense callback', () => {
     const {promise, resolveRef, PromiseComp} = createThenable();