expect: Improve report when matcher fails, part 13

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ### Features
 
+- `[expect]`: Improve report when matcher fails, part 13 ([#8077](https://github.com/facebook/jest/pull/8077))
 - `[@jest/core]` Filter API pre-filter setup hook ([#8142](https://github.com/facebook/jest/pull/8142))
 - `[jest-snapshot]` Improve report when matcher fails, part 14 ([#8132](https://github.com/facebook/jest/pull/8132))
 - `[@jest/reporter]` Display todo and skip test descriptions when verbose is true ([#8038](https://github.com/facebook/jest/pull/8038))

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

@@ -1198,84 +1198,114 @@ Received:    <red>34</>"
 `;
 
 exports[`.toBeInstanceOf() failing "a" and [Function String] 1`] = `
-"<dim>expect(</><red>value</><dim>).toBeInstanceOf(</><green>constructor</><dim>)</>
+"<dim>expect(</><red>received</><dim>).</>toBeInstanceOf<dim>(</><green>expected</><dim>)</>
 
 Expected constructor: <green>String</>
-Received constructor: <red>String</>
+Received value has no prototype
 Received value: <red>\\"a\\"</>"
 `;
 
+exports[`.toBeInstanceOf() failing /\\w+/ and [Function anonymous] 1`] = `
+"<dim>expect(</><red>received</><dim>).</>toBeInstanceOf<dim>(</><green>expected</><dim>)</>
+
+Expected constructor name is an empty string
+Received constructor: <red>RegExp</>
+Received value: <red>/\\\\w+/</>"
+`;
+
 exports[`.toBeInstanceOf() failing {} and [Function A] 1`] = `
-"<dim>expect(</><red>value</><dim>).toBeInstanceOf(</><green>constructor</><dim>)</>
+"<dim>expect(</><red>received</><dim>).</>toBeInstanceOf<dim>(</><green>expected</><dim>)</>
 
 Expected constructor: <green>A</>
-Received constructor: <red>undefined</>
+Received value has no prototype
 Received value: <red>{}</>"
 `;
 
 exports[`.toBeInstanceOf() failing {} and [Function B] 1`] = `
-"<dim>expect(</><red>value</><dim>).toBeInstanceOf(</><green>constructor</><dim>)</>
+"<dim>expect(</><red>received</><dim>).</>toBeInstanceOf<dim>(</><green>expected</><dim>)</>
 
 Expected constructor: <green>B</>
 Received constructor: <red>A</>
 Received value: <red>{}</>"
 `;
 
+exports[`.toBeInstanceOf() failing {} and [Function RegExp] 1`] = `
+"<dim>expect(</><red>received</><dim>).</>toBeInstanceOf<dim>(</><green>expected</><dim>)</>
+
+Expected constructor: <green>RegExp</>
+Received constructor name is an empty string
+Received value: <red>{}</>"
+`;
+
 exports[`.toBeInstanceOf() failing 1 and [Function Number] 1`] = `
-"<dim>expect(</><red>value</><dim>).toBeInstanceOf(</><green>constructor</><dim>)</>
+"<dim>expect(</><red>received</><dim>).</>toBeInstanceOf<dim>(</><green>expected</><dim>)</>
 
 Expected constructor: <green>Number</>
-Received constructor: <red>Number</>
+Received value has no prototype
 Received value: <red>1</>"
 `;
 
 exports[`.toBeInstanceOf() failing null and [Function String] 1`] = `
-"<dim>expect(</><red>value</><dim>).toBeInstanceOf(</><green>constructor</><dim>)</>
+"<dim>expect(</><red>received</><dim>).</>toBeInstanceOf<dim>(</><green>expected</><dim>)</>
 
 Expected constructor: <green>String</>
-Received constructor: 
+Received value has no prototype
 Received value: <red>null</>"
 `;
 
 exports[`.toBeInstanceOf() failing true and [Function Boolean] 1`] = `
-"<dim>expect(</><red>value</><dim>).toBeInstanceOf(</><green>constructor</><dim>)</>
+"<dim>expect(</><red>received</><dim>).</>toBeInstanceOf<dim>(</><green>expected</><dim>)</>
 
 Expected constructor: <green>Boolean</>
-Received constructor: <red>Boolean</>
+Received value has no prototype
 Received value: <red>true</>"
 `;
 
 exports[`.toBeInstanceOf() failing undefined and [Function String] 1`] = `
-"<dim>expect(</><red>value</><dim>).toBeInstanceOf(</><green>constructor</><dim>)</>
+"<dim>expect(</><red>received</><dim>).</>toBeInstanceOf<dim>(</><green>expected</><dim>)</>
 
 Expected constructor: <green>String</>
-Received constructor: 
+Received value has no prototype
 Received value: <red>undefined</>"
 `;
 
 exports[`.toBeInstanceOf() passing [] and [Function Array] 1`] = `
-"<dim>expect(</><red>value</><dim>).</>not<dim>.toBeInstanceOf(</><green>constructor</><dim>)</>
+"<dim>expect(</><red>received</><dim>).</>not<dim>.</>toBeInstanceOf<dim>(</><green>expected</><dim>)</>
 
-Expected constructor: <green>Array</>
+Expected constructor: not <green>Array</>
 Received value: <red>[]</>"
 `;
 
 exports[`.toBeInstanceOf() passing {} and [Function A] 1`] = `
-"<dim>expect(</><red>value</><dim>).</>not<dim>.toBeInstanceOf(</><green>constructor</><dim>)</>
+"<dim>expect(</><red>received</><dim>).</>not<dim>.</>toBeInstanceOf<dim>(</><green>expected</><dim>)</>
 
-Expected constructor: <green>A</>
+Expected constructor: not <green>A</>
+Received value: <red>{}</>"
+`;
+
+exports[`.toBeInstanceOf() passing {} and [Function B] 1`] = `
+"<dim>expect(</><red>received</><dim>).</>not<dim>.</>toBeInstanceOf<dim>(</><green>expected</><dim>)</>
+
+Expected constructor: not <green>B</>
+Received value: <red>{}</>"
+`;
+
+exports[`.toBeInstanceOf() passing {} and [Function name() {}] 1`] = `
+"<dim>expect(</><red>received</><dim>).</>not<dim>.</>toBeInstanceOf<dim>(</><green>expected</><dim>)</>
+
+Expected constructor name is not a string
 Received value: <red>{}</>"
 `;
 
 exports[`.toBeInstanceOf() passing Map {} and [Function Map] 1`] = `
-"<dim>expect(</><red>value</><dim>).</>not<dim>.toBeInstanceOf(</><green>constructor</><dim>)</>
+"<dim>expect(</><red>received</><dim>).</>not<dim>.</>toBeInstanceOf<dim>(</><green>expected</><dim>)</>
 
-Expected constructor: <green>Map</>
+Expected constructor: not <green>Map</>
 Received value: <red>Map {}</>"
 `;
 
 exports[`.toBeInstanceOf() throws if constructor is not a function 1`] = `
-"<dim>expect(</><red>received</><dim>).toBeInstanceOf(</><green>expected</><dim>)</>
+"<dim>expect(</><red>received</><dim>).</>toBeInstanceOf<dim>(</><green>expected</><dim>)</>
 
 <bold>Matcher error</>: <green>expected</> value must be a function
 

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

@@ -684,8 +684,28 @@ describe('.toEqual()', () => {
 describe('.toBeInstanceOf()', () => {
   class A {}
   class B {}
+  class C extends B {}
 
-  [[new Map(), Map], [[], Array], [new A(), A]].forEach(([a, b]) => {
+  class HasStaticNameMethod {
+    constructor() {}
+    static name() {}
+  }
+
+  function DefinesNameProp() {}
+  Object.defineProperty(DefinesNameProp, 'name', {
+    configurable: true,
+    enumerable: false,
+    value: '',
+    writable: true,
+  });
+
+  [
+    [new Map(), Map],
+    [[], Array],
+    [new A(), A],
+    [new C(), B], // subclass
+    [new HasStaticNameMethod(), HasStaticNameMethod],
+  ].forEach(([a, b]) => {
     test(`passing ${stringify(a)} and ${stringify(b)}`, () => {
       expect(() =>
         jestExpect(a).not.toBeInstanceOf(b),
@@ -703,6 +723,8 @@ describe('.toBeInstanceOf()', () => {
     [Object.create(null), A],
     [undefined, String],
     [null, String],
+    [/\w+/, function() {}],
+    [new DefinesNameProp(), RegExp],
   ].forEach(([a, b]) => {
     test(`failing ${stringify(a)} and ${stringify(b)}`, () => {
       expect(() =>

packages/expect/src/matchers.ts

@@ -6,7 +6,7 @@
  *
  */
 
-import getType from 'jest-get-type';
+import getType, {isPrimitive} from 'jest-get-type';
 import {
   EXPECTED_COLOR,
   RECEIVED_COLOR,
@@ -220,45 +220,62 @@ const matchers: MatchersObject = {
     return {message, pass};
   },
 
-  toBeInstanceOf(this: MatcherState, received: any, constructor: Function) {
-    const constType = getType(constructor);
+  toBeInstanceOf(this: MatcherState, received: any, expected: Function) {
+    const options: MatcherHintOptions = {
+      isNot: this.isNot,
+      promise: this.promise,
+    };
 
-    if (constType !== 'function') {
+    if (typeof expected !== 'function') {
       throw new Error(
         matcherErrorMessage(
-          matcherHint('.toBeInstanceOf', undefined, undefined, {
-            isNot: this.isNot,
-          }),
+          matcherHint('toBeInstanceOf', undefined, undefined, options),
           `${EXPECTED_COLOR('expected')} value must be a function`,
-          printWithType('Expected', constructor, printExpected),
+          printWithType('Expected', expected, printExpected),
         ),
       );
     }
-    const pass = received instanceof constructor;
+
+    const pass = received instanceof expected;
+
+    const NAME_IS_NOT_STRING = ' name is not a string\n';
+    const NAME_IS_EMPTY_STRING = ' name is an empty string\n';
 
     const message = pass
       ? () =>
-          matcherHint('.toBeInstanceOf', 'value', 'constructor', {
-            isNot: this.isNot,
-          }) +
+          matcherHint('toBeInstanceOf', undefined, undefined, options) +
           '\n\n' +
-          `Expected constructor: ${EXPECTED_COLOR(
-            constructor.name || String(constructor),
-          )}\n` +
+          // A truthy test for `expected.name` property has false positive for:
+          // function with a defined name property
+          // class with a static name method
+          (typeof expected.name !== 'string'
+            ? 'Expected constructor' + NAME_IS_NOT_STRING
+            : expected.name.length === 0
+            ? 'Expected constructor' + NAME_IS_EMPTY_STRING
+            : `Expected constructor: not ${EXPECTED_COLOR(expected.name)}\n`) +
           `Received value: ${printReceived(received)}`
       : () =>
-          matcherHint('.toBeInstanceOf', 'value', 'constructor', {
-            isNot: this.isNot,
-          }) +
+          matcherHint('toBeInstanceOf', undefined, undefined, options) +
           '\n\n' +
-          `Expected constructor: ${EXPECTED_COLOR(
-            constructor.name || String(constructor),
-          )}\n` +
-          `Received constructor: ${RECEIVED_COLOR(
-            received != null
-              ? received.constructor && received.constructor.name
-              : '',
-          )}\n` +
+          // A truthy test for `expected.name` property has false positive for:
+          // function with a defined name property
+          // class with a static name method
+          (typeof expected.name !== 'string'
+            ? 'Expected constructor' + NAME_IS_NOT_STRING
+            : expected.name.length === 0
+            ? 'Expected constructor' + NAME_IS_EMPTY_STRING
+            : `Expected constructor: ${EXPECTED_COLOR(expected.name)}\n`) +
+          (isPrimitive(received) || Object.getPrototypeOf(received) === null
+            ? 'Received value has no prototype\n'
+            : typeof received.constructor !== 'function'
+            ? ''
+            : typeof received.constructor.name !== 'string'
+            ? 'Received constructor' + NAME_IS_NOT_STRING
+            : received.constructor.name.length === 0
+            ? 'Received constructor' + NAME_IS_EMPTY_STRING
+            : `Received constructor: ${RECEIVED_COLOR(
+                received.constructor.name,
+              )}\n`) +
           `Received value: ${printReceived(received)}`;
 
     return {message, pass};