Introduce toStrictEqual

packages/expect/src/__tests__/matchers.test.js

@@ -204,6 +204,32 @@ describe('.toBe()', () => {
   });
 });
 
+describe('.toStrictEqual()', () => {
+  class TestClass {
+    constructor(a, b) {
+      this.a = a;
+      this.b = b;
+    }
+  }
+
+  expect({
+    test: new TestClass(1, 2),
+  }).toStrictEqual({test: new TestClass(1, 2)});
+});
+
+describe('.not.toStrictEqual()', () => {
+  class TestClass {
+    constructor(a, b) {
+      this.a = a;
+      this.b = b;
+    }
+  }
+
+  expect({
+    test: new TestClass(1, 2),
+  }).not.toStrictEqual({test: {a: 1, b: 2}});
+});
+
 describe('.toEqual()', () => {
   [
     [true, false],

packages/expect/src/matchers.js

@@ -29,6 +29,7 @@ import {
   getPath,
   iterableEquality,
   subsetEquality,
+  typeEquality,
 } from './utils';
 import {equals} from './jasmine_utils';
 
@@ -615,6 +616,38 @@ const matchers: MatchersObject = {
 
     return {message, pass};
   },
+
+  toStrictEqual(received: any, expected: any) {
+    const pass = equals(received, expected, [iterableEquality, typeEquality]);
+
+    const message = pass
+      ? () =>
+          matcherHint('.not.toStrictEqual') +
+          '\n\n' +
+          `Expected value to not equal:\n` +
+          `  ${printExpected(expected)}\n` +
+          `Received:\n` +
+          `  ${printReceived(received)}`
+      : () => {
+          const diffString = diff(expected, received, {
+            expand: this.expand,
+          });
+          return (
+            matcherHint('.toStrictEqual') +
+            '\n\n' +
+            `Expected value to equal:\n` +
+            `  ${printExpected(expected)}\n` +
+            `Received:\n` +
+            `  ${printReceived(received)}` +
+            (diffString ? `\n\nDifference:\n\n${diffString}` : '')
+          );
+        };
+
+    // Passing the the actual and expected objects so that a custom reporter
+    // could access them, for example in order to display a custom visual diff,
+    // or create a different error message
+    return {actual: received, expected, message, name: 'toStrictEqual', pass};
+  },
 };
 
 export default matchers;

packages/expect/src/utils.js

@@ -185,6 +185,14 @@ export const subsetEquality = (object: Object, subset: Object) => {
   );
 };
 
+export const typeEquality = (a: any, b: any) => {
+  if (a == null || b == null || a.constructor.name === b.constructor.name) {
+    return undefined;
+  }
+
+  return false;
+};
+
 export const partition = <T>(
   items: Array<T>,
   predicate: T => boolean,