feat: support async functions in toThrow

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

@@ -10,7 +10,7 @@ Resolved to value: <r>4</>
 exports[`.rejects fails non-promise value "a" 1`] = `
 <d>expect(</><r>received</><d>).</>rejects<d>.</>toBeDefined<d>()</>
 
-<b>Matcher error</>: <r>received</> value must be a promise
+<b>Matcher error</>: <r>received</> value must be a promise or an async function
 
 Received has type:  string
 Received has value: <r>"a"</>
@@ -19,7 +19,7 @@ Received has value: <r>"a"</>
 exports[`.rejects fails non-promise value [1] 1`] = `
 <d>expect(</><r>received</><d>).</>rejects<d>.</>toBeDefined<d>()</>
 
-<b>Matcher error</>: <r>received</> value must be a promise
+<b>Matcher error</>: <r>received</> value must be a promise or an async function
 
 Received has type:  array
 Received has value: <r>[1]</>
@@ -28,7 +28,7 @@ Received has value: <r>[1]</>
 exports[`.rejects fails non-promise value [Function anonymous] 1`] = `
 <d>expect(</><r>received</><d>).</>rejects<d>.</>toBeDefined<d>()</>
 
-<b>Matcher error</>: <r>received</> value must be a promise
+<b>Matcher error</>: <r>received</> value must be a promise or an async function
 
 Received has type:  function
 Received has value: <r>[Function anonymous]</>
@@ -37,7 +37,7 @@ Received has value: <r>[Function anonymous]</>
 exports[`.rejects fails non-promise value {"a": 1} 1`] = `
 <d>expect(</><r>received</><d>).</>rejects<d>.</>toBeDefined<d>()</>
 
-<b>Matcher error</>: <r>received</> value must be a promise
+<b>Matcher error</>: <r>received</> value must be a promise or an async function
 
 Received has type:  object
 Received has value: <r>{"a": 1}</>
@@ -46,7 +46,7 @@ Received has value: <r>{"a": 1}</>
 exports[`.rejects fails non-promise value 4 1`] = `
 <d>expect(</><r>received</><d>).</>rejects<d>.</>not<d>.</>toBeDefined<d>()</>
 
-<b>Matcher error</>: <r>received</> value must be a promise
+<b>Matcher error</>: <r>received</> value must be a promise or an async function
 
 Received has type:  number
 Received has value: <r>4</>
@@ -55,15 +55,15 @@ Received has value: <r>4</>
 exports[`.rejects fails non-promise value null 1`] = `
 <d>expect(</><r>received</><d>).</>rejects<d>.</>not<d>.</>toBeDefined<d>()</>
 
-<b>Matcher error</>: <r>received</> value must be a promise
+<b>Matcher error</>: <r>received</> value must be a promise or an async function
 
 Received has value: <r>null</>
 `;
 
 exports[`.rejects fails non-promise value true 1`] = `
 <d>expect(</><r>received</><d>).</>rejects<d>.</>not<d>.</>toBeDefined<d>()</>
 
-<b>Matcher error</>: <r>received</> value must be a promise
+<b>Matcher error</>: <r>received</> value must be a promise or an async function
 
 Received has type:  boolean
 Received has value: <r>true</>
@@ -72,7 +72,7 @@ Received has value: <r>true</>
 exports[`.rejects fails non-promise value undefined 1`] = `
 <d>expect(</><r>received</><d>).</>rejects<d>.</>not<d>.</>toBeDefined<d>()</>
 
-<b>Matcher error</>: <r>received</> value must be a promise
+<b>Matcher error</>: <r>received</> value must be a promise or an async function
 
 Received has value: <r>undefined</>
 `;

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

@@ -55,7 +55,11 @@ describe('.rejects', () => {
     }
     await jestExpect(fn()).rejects.toThrow('some error');
   });
-
+  it('should reject async function to toThrow', async () => {
+    await expect(async () => {
+      throw new Error('Test');
+    }).rejects.toThrow('Test');
+  });
   ['a', [1], () => {}, {a: 1}].forEach(value => {
     it(`fails non-promise value ${stringify(value)} synchronously`, () => {
       let error;
@@ -101,7 +105,6 @@ describe('.rejects', () => {
       expect(error.message).toMatchSnapshot();
     });
   });
-
   it('fails for promise that resolves', async () => {
     let error;
     try {

packages/expect/src/index.ts

@@ -9,6 +9,7 @@
 import * as matcherUtils from 'jest-matcher-utils';
 import type {
   AsyncExpectationResult,
+  AsyncFunction,
   Expect,
   ExpectationResult,
   MatcherState as JestMatcherState,
@@ -57,6 +58,9 @@ const isPromise = <T extends any>(obj: any): obj is PromiseLike<T> =>
   (typeof obj === 'object' || typeof obj === 'function') &&
   typeof obj.then === 'function';
 
+const isAsyncFunction = (fn: any): boolean =>
+  !!fn && fn.constructor && fn.constructor.name == 'AsyncFunction';
+
 const createToThrowErrorMatchingSnapshotMatcher = function (
   matcher: RawMatcherFn,
 ) {
@@ -189,31 +193,40 @@ const makeRejectMatcher = (
   matcherName: string,
   matcher: RawMatcherFn,
   isNot: boolean,
-  actual: Promise<any>,
+  actual: Promise<any> | AsyncFunction,
   outerErr: JestAssertionError,
 ): PromiseMatcherFn => (...args) => {
   const options = {
     isNot,
     promise: 'rejects',
   };
+  let actualWrapper: Promise<any>;
 
   if (!isPromise(actual)) {
-    throw new JestAssertionError(
-      matcherUtils.matcherErrorMessage(
-        matcherUtils.matcherHint(matcherName, undefined, '', options),
-        `${matcherUtils.RECEIVED_COLOR('received')} value must be a promise`,
-        matcherUtils.printWithType(
-          'Received',
-          actual,
-          matcherUtils.printReceived,
+    if (!isAsyncFunction(actual)) {
+      throw new JestAssertionError(
+        matcherUtils.matcherErrorMessage(
+          matcherUtils.matcherHint(matcherName, undefined, '', options),
+          `${matcherUtils.RECEIVED_COLOR(
+            'received',
+          )} value must be a promise or an async function`,
+          matcherUtils.printWithType(
+            'Received',
+            actual,
+            matcherUtils.printReceived,
+          ),
         ),
-      ),
-    );
+      );
+    } else {
+      actualWrapper = Promise.resolve().then(actual);
+    }
+  } else {
+    actualWrapper = actual;
   }
 
   const innerErr = new JestAssertionError();
 
-  return actual.then(
+  return actualWrapper.then(
     result => {
       outerErr.message =
         matcherUtils.matcherHint(matcherName, undefined, '', options) +

packages/expect/src/types.ts

@@ -16,6 +16,8 @@ export type SyncExpectationResult = {
 
 export type AsyncExpectationResult = Promise<SyncExpectationResult>;
 
+export type AsyncFunction = (...args: Array<any>) => Promise<any>;
+
 export type ExpectationResult = SyncExpectationResult | AsyncExpectationResult;
 
 export type RawMatcherFn = {