[jest] add mock result type

types/jest/index.d.ts

@@ -976,20 +976,29 @@ declare namespace jest {
     }
 
     /**
-     * Represents the result of a single call to a mock function.
+     * Represents the result of a single call to a mock function with a return value.
      */
-    interface MockResult {
-        /**
-         * True if the function threw.
-         * False if the function returned.
-         */
-        isThrow: boolean;
-        /**
-         * The value that was either thrown or returned by the function.
-         */
+    interface MockResultReturn<T> {
+        type: 'return';
+        value: T;
+    }
+    /**
+     * Represents the result of a single incomplete call to a mock function.
+     */
+    interface MockResultIncomplete {
+        type: 'incomplete';
+        value: undefined;
+    }
+    /**
+     * Represents the result of a single call to a mock function with a thrown error.
+     */
+    interface MockResultThrow {
+        type: 'throw';
         value: any;
     }
 
+    type MockResult<T> = MockResultReturn<T> | MockResultThrow | MockResultIncomplete;
+
     interface MockContext<T, Y extends any[]> {
         calls: Y[];
         instances: T[];
@@ -997,7 +1006,7 @@ declare namespace jest {
         /**
          * List of results of calls to the mock function.
          */
-        results: MockResult[];
+        results: Array<MockResult<T>>;
     }
 }
 

types/jest/jest-tests.ts

@@ -480,6 +480,19 @@ mocked.test4.mockRejectedValue(new Error());
 // $ExpectError
 mocked.test4.mockRejectedValueOnce(new Error());
 
+const mockResult = jest.fn(() => 1).mock.results[0];
+switch (mockResult.type) {
+    case 'return':
+        mockResult.value; // $ExpectType number
+        break;
+    case 'incomplete':
+        mockResult.value; // $ExpectType undefined
+        break;
+    case 'throw':
+        mockResult.value; // $ExpectType any
+        break;
+}
+
 /* Snapshot serialization */
 
 const snapshotSerializerPlugin: jest.SnapshotSerializerPlugin = {