test: add more isLoading tests for the case a key is null or an error

test/use-swr-loading.test.tsx

@@ -321,14 +321,24 @@ describe('useSWR - loading', () => {
   it('isLoading and isValidating should always respect cache value', async () => {
     const key = createKey()
     const Page = () => {
-      const { data } = useSWR(key, () => createResponse('result', { delay: 10 }))
-      const { data: response } = useSWR(data, () => createResponse('data', { delay: 10 }))
+      const { data } = useSWR(key, () =>
+        createResponse('result', { delay: 10 })
+      )
+      const { data: response } = useSWR(data, () =>
+        createResponse('data', { delay: 10 })
+      )
       // eslint-disable-next-line react/display-name
       const Component = ((_: any) => () => {
-        // eslint-disable-next-line react-hooks/rules-of-hooks
-        const { data: result, isLoading, isValidating } = useSWR(key, () => createResponse('result', { delay: 10 }))
+        const {
+          data: result,
+          isLoading,
+          isValidating
+          // eslint-disable-next-line react-hooks/rules-of-hooks
+        } = useSWR(key, () => createResponse('result', { delay: 10 }))
         return (
-          <div>{`result is ${result ? result : 'null'},${isLoading},${isValidating}`}</div>
+          <div>{`result is ${
+            result ? result : 'null'
+          },${isLoading},${isValidating}`}</div>
         )
       })(response)
       return <Component></Component>
@@ -337,4 +347,29 @@ describe('useSWR - loading', () => {
     screen.getByText('result is null,true,true')
     await screen.findByText('result is result,false,false')
   })
+
+  it('isLoading should be false when key is null', () => {
+    function Page() {
+      const { isLoading } = useSWR(null, () => 'data')
+      return <div>isLoading:{String(isLoading)}</div>
+    }
+
+    renderWithConfig(<Page />)
+    screen.getByText('isLoading:false')
+  })
+
+  it('isLoading should be false when the key function throws an error', () => {
+    function Page() {
+      const { isLoading } = useSWR(
+        () => {
+          throw new Error('error')
+        },
+        () => 'data'
+      )
+      return <div>isLoading:{String(isLoading)}</div>
+    }
+
+    renderWithConfig(<Page />)
+    screen.getByText('isLoading:false')
+  })
 })