[Fix] improve "bad adapter" error message

Fixes #1437

packages/enzyme-test-suite/test/Adapter-spec.jsx

@@ -2,8 +2,10 @@ import React from 'react';
 import { expect } from 'chai';
 import jsdom from 'jsdom';
 import configuration from 'enzyme/build/configuration';
+import { configure, shallow } from 'enzyme';
 
 import './_helpers/setupAdapters';
+import Adapter from './_helpers/adapter';
 import { renderToString } from './_helpers/react-compat';
 import { REACT013, REACT16 } from './_helpers/version';
 import { itIf, describeWithDOM } from './_helpers';
@@ -36,8 +38,30 @@ function cleanNode(node) {
 }
 
 describe('Adapter', () => {
-  describeWithDOM('mounted render', () => {
+  describe('error message', () => {
+    afterEach(() => {
+      configure({ adapter });
+    });
+
+    it('fails to render when no adapter is configured', () => {
+      configure({ adapter: undefined });
+      expect(() => shallow(<div />)).to.throw(Error, /Enzyme expects an adapter to be configured, but found none/);
+    });
 
+    it('fails to render when an object that does not inherit from the base class is configured', () => {
+      expect(() => configure({ adapter: {} })).to.throw(Error, /configured enzyme adapter did not inherit from the EnzymeAdapter base class/);
+    });
+
+    it('fails to render when an adapter constructor is configured', () => {
+      expect(() => configure({ adapter: Adapter })).to.throw(Error, /you provided an adapter \*constructor\*/);
+    });
+
+    it('fails to render when a non-adapter-constructor function is configured', () => {
+      expect(() => configure({ adapter() {} })).to.throw(Error, /an enzyme adapter must be an object instance; you provided a function/);
+    });
+  });
+
+  describeWithDOM('mounted render', () => {
     function hydratedTreeMatchesUnhydrated(element) {
       const markup = renderToString(element);
       const dom = jsdom.jsdom(`<div id="root">${markup}</div>`);
@@ -763,5 +787,4 @@ describe('Adapter', () => {
       },
     }));
   });
-
 });

packages/enzyme-test-suite/test/_helpers/adapter.js

@@ -0,0 +1,29 @@
+/* eslint global-require: 0, import/no-extraneous-dependencies: 0, import/no-unresolved: 0 */
+/**
+ * This file is needed only because we run our unit tests on multiple
+ * versions of React at a time. This file basically figures out which
+ * version of React is loaded, and exports the correct adapter for configuring.
+ */
+const {
+  REACT013,
+  REACT014,
+  REACT15,
+  REACT155,
+  REACT16,
+} = require('./version');
+
+let Adapter = null;
+
+if (REACT013) {
+  Adapter = require('enzyme-adapter-react-13');
+} else if (REACT014) {
+  Adapter = require('enzyme-adapter-react-14');
+} else if (REACT155) {
+  Adapter = require('enzyme-adapter-react-15');
+} else if (REACT15) {
+  Adapter = require('enzyme-adapter-react-15.4');
+} else if (REACT16) {
+  Adapter = require('enzyme-adapter-react-16');
+}
+
+module.exports = Adapter;

packages/enzyme-test-suite/test/_helpers/setupAdapters.js

@@ -1,31 +1,4 @@
-/* eslint global-require: 0, import/no-extraneous-dependencies: 0, import/no-unresolved: 0 */
-/**
- * This file is needed only because we run our unit tests on multiple
- * versions of React at a time. This file basically figures out which
- * version of React is loaded, and configures enzyme to use the right
- * corresponding adapter.
- */
-const {
-  REACT013,
-  REACT014,
-  REACT15,
-  REACT155,
-  REACT16,
-} = require('./version');
 const Enzyme = require('enzyme');
-
-let Adapter = null;
-
-if (REACT013) {
-  Adapter = require('enzyme-adapter-react-13');
-} else if (REACT014) {
-  Adapter = require('enzyme-adapter-react-14');
-} else if (REACT155) {
-  Adapter = require('enzyme-adapter-react-15');
-} else if (REACT15) {
-  Adapter = require('enzyme-adapter-react-15.4');
-} else if (REACT16) {
-  Adapter = require('enzyme-adapter-react-16');
-}
+const Adapter = require('./adapter');
 
 Enzyme.configure({ adapter: new Adapter() });

packages/enzyme/src/validateAdapter.js

@@ -3,8 +3,34 @@ import EnzymeAdapter from './EnzymeAdapter';
 export default function validateAdapter(adapter) {
   if (!adapter) {
     throw new Error(`
-      Enzyme Internal Error: Enzyme expects an adapter to be configured, but found none. To
-      configure an adapter, you should call \`Enzyme.configure({ adapter: new Adapter() })\`
+      Enzyme Internal Error: Enzyme expects an adapter to be configured, but found none.
+      To configure an adapter, you should call \`Enzyme.configure({ adapter: new Adapter() })\`
+      before using any of Enzyme's top level APIs, where \`Adapter\` is the adapter
+      corresponding to the library currently being tested. For example:
+
+      import Adapter from 'enzyme-adapter-react-15';
+
+      To find out more about this, see http://airbnb.io/enzyme/docs/installation/index.html
+    `);
+  }
+  if (typeof adapter === 'function') {
+    if (Object.getPrototypeOf(adapter) === EnzymeAdapter) {
+      throw new Error(`
+        Enzyme Internal Error: Enzyme expects an adapter instance to be configured -
+        you provided an adapter *constructor*.
+        To configure an adapter, you should call \`Enzyme.configure({ adapter: new Adapter() })\`
+        before using any of Enzyme's top level APIs, where \`Adapter\` is the adapter
+        corresponding to the library currently being tested. For example:
+
+        import Adapter from 'enzyme-adapter-react-15';
+
+        To find out more about this, see http://airbnb.io/enzyme/docs/installation/index.html
+      `);
+    }
+    throw new Error(`
+      Enzyme Internal Error: Enzyme expects an adapter to be configured -
+      an enzyme adapter must be an object instance; you provided a function.
+      To configure an adapter, you should call \`Enzyme.configure({ adapter: new Adapter() })\`
       before using any of Enzyme's top level APIs, where \`Adapter\` is the adapter
       corresponding to the library currently being tested. For example: