feat: add a '.toBeEmptyObject()' custom matcher. (#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;
  }
 }