Improved DevTools context test harness (facebook#19878)

Author: Brian Vaughn

packages/react-devtools-shell/src/app/InspectableElements/Contexts.js

@@ -8,11 +8,19 @@
  */
 
 import * as React from 'react';
-import {createContext, Component, Fragment, useContext} from 'react';
+import {createContext, Component, useContext} from 'react';
 import PropTypes from 'prop-types';
 
 function someNamedFunction() {}
 
+function formatContextForDisplay(name, value) {
+  return (
+    <li>
+      {name}: <pre>{JSON.stringify(value, null, 2)}</pre>
+    </li>
+  );
+}
+
 const contextData = {
   array: ['first', 'second', 'third'],
   bool: true,
@@ -61,7 +69,7 @@ class LegacyContextConsumer extends Component<any> {
   };
 
   render() {
-    return null;
+    return formatContextForDisplay('LegacyContextConsumer', this.context);
   }
 }
 
@@ -88,34 +96,55 @@ class ModernContextType extends Component<any> {
   static contextType = ModernContext;
 
   render() {
-    return null;
+    return formatContextForDisplay('ModernContextType', this.context);
   }
 }
 
 function FunctionalContextConsumer() {
-  useContext(StringContext);
-  return null;
+  const value = useContext(StringContext);
+  return formatContextForDisplay('FunctionalContextConsumer', value);
 }
 
 export default function Contexts() {
   return (
-    <Fragment>
-      <LegacyContextProvider>
-        <LegacyContextConsumer />
-      </LegacyContextProvider>
-      <ModernContext.Provider value={contextData}>
-        <ModernContext.Consumer>{value => null}</ModernContext.Consumer>
-        <ModernContextType />
-      </ModernContext.Provider>
-      <FunctionalContextConsumer />
-      <ArrayContext.Consumer>{value => null}</ArrayContext.Consumer>
-      <BoolContext.Consumer>{value => null}</BoolContext.Consumer>
-      <FuncContext.Consumer>{value => null}</FuncContext.Consumer>
-      <NumberContext.Consumer>{value => null}</NumberContext.Consumer>
-      <StringContext.Consumer>{value => null}</StringContext.Consumer>
-      <SymbolContext.Consumer>{value => null}</SymbolContext.Consumer>
-      <NullContext.Consumer>{value => null}</NullContext.Consumer>
-      <UndefinedContext.Consumer>{value => null}</UndefinedContext.Consumer>
-    </Fragment>
+    <div>
+      <h1>Contexts</h1>
+      <ul>
+        <LegacyContextProvider>
+          <LegacyContextConsumer />
+        </LegacyContextProvider>
+        <ModernContext.Provider value={contextData}>
+          <ModernContext.Consumer>
+            {value => formatContextForDisplay('ModernContext.Consumer', value)}
+          </ModernContext.Consumer>
+          <ModernContextType />
+        </ModernContext.Provider>
+        <FunctionalContextConsumer />
+        <ArrayContext.Consumer>
+          {value => formatContextForDisplay('ArrayContext.Consumer', value)}
+        </ArrayContext.Consumer>
+        <BoolContext.Consumer>
+          {value => formatContextForDisplay('BoolContext.Consumer', value)}
+        </BoolContext.Consumer>
+        <FuncContext.Consumer>
+          {value => formatContextForDisplay('FuncContext.Consumer', value)}
+        </FuncContext.Consumer>
+        <NumberContext.Consumer>
+          {value => formatContextForDisplay('NumberContext.Consumer', value)}
+        </NumberContext.Consumer>
+        <StringContext.Consumer>
+          {value => formatContextForDisplay('StringContext.Consumer', value)}
+        </StringContext.Consumer>
+        <SymbolContext.Consumer>
+          {value => formatContextForDisplay('SymbolContext.Consumer', value)}
+        </SymbolContext.Consumer>
+        <NullContext.Consumer>
+          {value => formatContextForDisplay('NullContext.Consumer', value)}
+        </NullContext.Consumer>
+        <UndefinedContext.Consumer>
+          {value => formatContextForDisplay('UndefinedContext.Consumer', value)}
+        </UndefinedContext.Consumer>
+      </ul>
+    </div>
   );
 }