From db657c7ba99742928e3f0547110bce2527b6a89c Mon Sep 17 00:00:00 2001
From: Simen Bekkhus <sbekkhus91@gmail.com>
Date: Sun, 23 Apr 2017 10:16:06 +0200
Subject: [PATCH] Support setting returnvalue from mock to `undefined`

Fixes #3320
---
 .../jest-mock/src/__tests__/jest-mock-test.js | 20 +++++++++++++++++++
 packages/jest-mock/src/index.js               |  2 ++
 2 files changed, 22 insertions(+)

diff --git a/packages/jest-mock/src/__tests__/jest-mock-test.js b/packages/jest-mock/src/__tests__/jest-mock-test.js
index 9c9897e914d2..5265812cfcb4 100644
--- a/packages/jest-mock/src/__tests__/jest-mock-test.js
+++ b/packages/jest-mock/src/__tests__/jest-mock-test.js
@@ -330,6 +330,26 @@ describe('moduleMocker', () => {
         expect(fn2()).not.toEqual('abcd');
       });
     });
+
+    it('supports mock value returning undefined', () => {
+      const obj = {
+        func: () => 'some text',
+      };
+
+      moduleMocker.spyOn(obj, 'func').mockReturnValue(undefined);
+
+      expect(obj.func()).not.toEqual('some text');
+    });
+
+    it('supports mock value once returning undefined', () => {
+      const obj = {
+        func: () => 'some text',
+      };
+
+      moduleMocker.spyOn(obj, 'func').mockReturnValueOnce(undefined);
+
+      expect(obj.func()).not.toEqual('some text');
+    });
   });
 
   describe('getMockImplementation', () => {
diff --git a/packages/jest-mock/src/index.js b/packages/jest-mock/src/index.js
index 9627e65e43c7..ba7001b9b30e 100644
--- a/packages/jest-mock/src/index.js
+++ b/packages/jest-mock/src/index.js
@@ -274,6 +274,8 @@ class ModuleMockerClass {
           if (returnValue === undefined) {
             returnValue = mockConfig.defaultReturnValue;
           }
+
+          return returnValue;
         }
 
         // If mockImplementationOnce()/mockImplementation() is last set,