feat: add a '.toBeEmptyObject()' custom matcher. (jest-community#255)

README.md

@@ -81,6 +81,7 @@ If you've come here to help contribute - Thanks! Take a look at the [contributin
     - [.toBeInteger()](#tobeinteger)
   - [Object](#object)
     - [.toBeObject()](#tobeobject)
+    - [.toBeEmptyObject()](#tobeemptyobject)
     - [.toContainKey(key)](#tocontainkeykey)
     - [.toContainKeys([keys])](#tocontainkeyskeys)
     - [.toContainAllKeys([keys])](#tocontainallkeyskeys)
@@ -589,6 +590,17 @@ test('passes when value is an integer', () => {
 
 ### Object
 
+#### .toBeEmptyObject()
+
+Use `.toBeEmptyObject` when checking if a value is an empty `Object`.
+
+```js
+test('passes when value is an empty object', () => {
+  expect({}).toBeEmptyObject();
+  expect({ a: 'hello' }).not.toBeEmptyObject();
+});
+```
+
 #### .toBeObject()
 
 Use `.toBeObject` when checking if a value is an `Object`.

src/matchers/toBeEmptyObject/__snapshots__/index.test.js.snap

@@ -0,0 +1,15 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`.not.toBeEmptyObject fails when given an empty object 1`] = `
+"<dim>expect(</><red>received</><dim>).not.toBeEmptyObject()</>
+
+Expected value to not be an empty object, received:
+  <red>{}</>"
+`;
+
+exports[`.toBeEmptyObject fails when not given an empty object 1`] = `
+"<dim>expect(</><red>received</><dim>).toBeEmptyObject()</>
+
+Expected value to be an empty object, received:
+  <red>{\\"property1\\": \\"something\\"}</>"
+`;

src/matchers/toBeEmptyObject/index.js

@@ -0,0 +1,26 @@
+import { matcherHint, printReceived } from 'jest-matcher-utils';
+
+import predicate from './predicate';
+
+const passMessage = received => () =>
+  matcherHint('.not.toBeEmptyObject', 'received', '') +
+  '\n\n' +
+  'Expected value to not be an empty object, received:\n' +
+  `  ${printReceived(received)}`;
+
+const failMessage = received => () =>
+  matcherHint('.toBeEmptyObject', 'received', '') +
+  '\n\n' +
+  'Expected value to be an empty object, received:\n' +
+  `  ${printReceived(received)}`;
+
+export default {
+  toBeEmptyObject: expected => {
+    const pass = predicate(expected);
+    if (pass) {
+      return { pass: true, message: passMessage(expected) };
+    }
+
+    return { pass: false, message: failMessage(expected) };
+  },
+};

src/matchers/toBeEmptyObject/index.test.js

@@ -0,0 +1,23 @@
+import matcher from './';
+
+expect.extend(matcher);
+
+describe('.toBeEmptyObject', () => {
+  test('passes when given an empty object', () => {
+    expect({}).toBeEmptyObject();
+  });
+
+  test('fails when not given an empty object', () => {
+    expect(() => expect({ property1: 'something' }).toBeEmptyObject()).toThrowErrorMatchingSnapshot();
+  });
+});
+
+describe('.not.toBeEmptyObject', () => {
+  test('passes when not given an empty object', () => {
+    expect({ property1: 'something' }).not.toBeEmptyObject();
+  });
+
+  test('fails when given an empty object', () => {
+    expect(() => expect({}).not.toBeEmptyObject()).toThrowErrorMatchingSnapshot();
+  });
+});

src/matchers/toBeEmptyObject/predicate.js

@@ -0,0 +1,3 @@
+import { getType } from 'jest-get-type';
+
+export default expected => getType(expected) === 'object' && Object.keys(expected).length === 0;

src/matchers/toBeEmptyObject/predicate.test.js

@@ -0,0 +1,11 @@
+import predicate from './predicate';
+
+describe('toBeEmptyObject Predicate', () => {
+  test('returns true when given an empty object', () => {
+    expect(predicate({})).toBe(true);
+  });
+
+  test('returns false when given a non-empty object', () => {
+    expect(predicate({ property1: 'something' })).toBe(false);
+  });
+});

types/index.d.ts

@@ -716,5 +716,10 @@ declare namespace jest {
      * @param {String | RegExp} message
      */
     toThrowWithMessage(type: Function, message: string | RegExp): any;
+
+    /**
+     * Use `.toBeEmptyObject` when checking if a value is an empty `Object`.
+     */
+    toBeEmptyObject(): R;
   }
 }