test: add toWarnDev custom Jest matcher

jest.config.js

@@ -6,7 +6,7 @@ module.exports = {
     '<rootDir>/dist*',
     '<rootDir>/functional-tests',
   ],
-  setupFilesAfterEnv: ['./scripts/jestInit.js'],
+  setupFilesAfterEnv: ['./scripts/jest/init.js'],
   watchPlugins: [
     'jest-watch-typeahead/filename',
     'jest-watch-typeahead/testname',

package.json

@@ -78,6 +78,7 @@
     "@types/enzyme": "^3.1.15",
     "@types/enzyme-adapter-react-16": "^1.0.3",
     "@types/jest": "^24.0.0",
+    "@types/jest-diff": "^20.0.1",
     "@types/lodash": "^4.14.120",
     "@types/react": "^16.7.20",
     "@types/react-dom": "^16.0.11",
@@ -113,6 +114,7 @@
     "express": "4.16.4",
     "inquirer": "6.2.2",
     "jest": "24.1.0",
+    "jest-diff": "24.0.0",
     "jest-watch-typeahead": "0.2.1",
     "jsdom-global": "3.0.2",
     "json": "9.0.6",

scripts/jestInit.js → scripts/jest/init.js

@@ -1,6 +1,8 @@
 import Enzyme from 'enzyme';
 import Adapter from 'enzyme-adapter-react-16';
 import { createSerializer } from 'enzyme-to-json';
+import { toWarnDev } from './matchers';
 
 Enzyme.configure({ adapter: new Adapter() });
 expect.addSnapshotSerializer(createSerializer({ mode: 'deep' }));
+expect.extend(toWarnDev);

scripts/jest/matchers/__tests__/toWarnDev-test.ts

@@ -0,0 +1,50 @@
+/* tslint:disable:no-console */
+
+describe('toWarnDev', () => {
+  describe('usage', () => {
+    test('fails with incorrect type of message', () => {
+      expect(() => {
+        // @ts-ignore:next-line
+        expect(() => {}).toWarnDev(false);
+      }).toThrowErrorMatchingInlineSnapshot(
+        `"toWarnDev() requires a parameter of type string but was given boolean."`
+      );
+    });
+  });
+
+  if (__DEV__) {
+    describe('without message', () => {
+      test('does not fail if called', () => {
+        expect(() => {
+          expect(() => {
+            console.warn('warning');
+          }).toWarnDev();
+        }).not.toThrow();
+      });
+
+      test('fails if not called', () => {
+        expect(() => {
+          expect(() => {}).toWarnDev();
+        }).toThrowErrorMatchingInlineSnapshot(`"No warning recorded."`);
+      });
+    });
+
+    describe('with message', () => {
+      test('does not fail with correct message', () => {
+        expect(() => {
+          expect(() => {
+            console.warn('warning');
+          }).toWarnDev('warning');
+        }).not.toThrow();
+      });
+
+      test('fails if a warning is not correct', () => {
+        expect(() => {
+          expect(() => {
+            console.warn('warning');
+          }).toWarnDev('another warning');
+        }).toThrow(/Unexpected warning recorded./);
+      });
+    });
+  }
+});

scripts/jest/matchers/index.ts

@@ -0,0 +1 @@
+export { default as toWarnDev } from './toWarnDev';

scripts/jest/matchers/toWarnDev.ts

@@ -0,0 +1,64 @@
+/* tslint:disable:no-console */
+import jestDiff from 'jest-diff';
+
+declare global {
+  namespace jest {
+    interface Matchers<R> {
+      toWarnDev(expectedMessage?: string): R;
+    }
+  }
+}
+
+const matcher = {
+  toWarnDev: (callback: () => void, expectedMessage: string) => {
+    if (expectedMessage !== undefined && typeof expectedMessage !== 'string') {
+      throw new Error(
+        `toWarnDev() requires a parameter of type string but was given ${typeof expectedMessage}.`
+      );
+    }
+
+    if (!__DEV__) {
+      callback();
+
+      return { pass: true };
+    }
+
+    const originalWarnMethod = console.warn;
+    let calledTimes = 0;
+    let actualWarning = '';
+
+    console.warn = (message: string) => {
+      calledTimes++;
+      actualWarning = message;
+    };
+
+    callback();
+
+    console.warn = originalWarnMethod;
+
+    // Expectation without any message.
+    // We only check that `console.warn` was called.
+    if (expectedMessage === undefined && calledTimes === 0) {
+      return {
+        pass: false,
+        message: () => 'No warning recorded.',
+      };
+    }
+
+    // Expectation with a message.
+    if (expectedMessage !== undefined && actualWarning !== expectedMessage) {
+      return {
+        pass: false,
+        message: () => `Unexpected warning recorded.
+
+Difference:
+
+${jestDiff(expectedMessage, actualWarning)}`,
+      };
+    }
+
+    return { pass: true };
+  },
+};
+
+export default matcher;

tslint.json

@@ -11,6 +11,7 @@
     "object-literal-sort-keys": false,
     "ordered-imports": false,
     "prettier": true,
-    "jsx-no-lambda": false
+    "jsx-no-lambda": false,
+    "no-empty": false
   }
 }

yarn.lock

@@ -1375,6 +1375,11 @@
     "@types/minimatch" "*"
     "@types/node" "*"
 
+"@types/jest-diff@^20.0.1":
+  version "20.0.1"
+  resolved "https://registry.yarnpkg.com/@types/jest-diff/-/jest-diff-20.0.1.tgz#35cc15b9c4f30a18ef21852e255fdb02f6d59b89"
+  integrity sha512-yALhelO3i0hqZwhjtcr6dYyaLoCHbAMshwtj6cGxTvHZAKXHsYGdff6E8EPw3xLKY0ELUTQ69Q1rQiJENnccMA==
+
 "@types/jest@^24.0.0":
   version "24.0.1"
   resolved "https://registry.yarnpkg.com/@types/jest/-/jest-24.0.1.tgz#8945411140e7cdfd5ea76380e5f5fa7bf17646ea"
@@ -7028,7 +7033,7 @@ jest-config@^24.1.0:
     pretty-format "^24.0.0"
     realpath-native "^1.0.2"
 
-jest-diff@^24.0.0:
+jest-diff@24.0.0, jest-diff@^24.0.0:
   version "24.0.0"
   resolved "https://registry.yarnpkg.com/jest-diff/-/jest-diff-24.0.0.tgz#a3e5f573dbac482f7d9513ac9cfa21644d3d6b34"
   integrity sha512-XY5wMpRaTsuMoU+1/B2zQSKQ9RdE9gsLkGydx3nvApeyPijLA8GtEvIcPwISRCer+VDf9W1mStTYYq6fPt8ryA==