From 4950dd9792c5d1da401a846ba408bf275f58e332 Mon Sep 17 00:00:00 2001
From: winh <winnie@gitlab.com>
Date: Thu, 11 May 2017 10:19:20 +0200
Subject: Document Promise testing best practice (!11284)

---
 doc/development/fe_guide/testing.md | 62 +++++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)

diff --git a/doc/development/fe_guide/testing.md b/doc/development/fe_guide/testing.md
index 5852cac2aa5..5c6bdc97ef6 100644
--- a/doc/development/fe_guide/testing.md
+++ b/doc/development/fe_guide/testing.md
@@ -68,6 +68,68 @@ describe('.methodName', () => {
   });
 });
 ```
+#### Testing Promises
+
+When testing Promises you should always make sure that the test is asynchronous and rejections are handled.
+Your Promise chain should therefore end with a call of the `done` callback and `done.fail` in case an error occurred.
+
+```javascript
+/// Good
+it('tests a promise', (done) => {
+  promise
+    .then((data) => {
+      expect(data).toBe(asExpected);
+    })
+    .then(done)
+    .catch(done.fail);
+});
+
+/// Good
+it('tests a promise rejection', (done) => {
+  promise
+    .catch((error) => {
+      expect(error).toBe(expectedError);
+    })
+    .then(done)
+    .catch(done.fail);
+});
+
+/// Bad (missing done callback)
+it('tests a promise', () => {
+  promise
+    .then((data) => {
+      expect(data).toBe(asExpected);
+    })
+});
+
+/// Bad (missing catch)
+it('tests a promise', (done) => {
+  promise
+    .then((data) => {
+      expect(data).toBe(asExpected);
+    })
+    .then(done)
+});
+
+/// Bad (use done.fail in asynchronous tests)
+it('tests a promise', (done) => {
+  promise
+    .then((data) => {
+      expect(data).toBe(asExpected);
+    })
+    .then(done)
+    .catch(fail)
+});
+
+/// Bad (missing catch)
+it('tests a promise rejection', (done) => {
+  promise
+    .catch((error) => {
+      expect(error).toBe(expectedError);
+    })
+    .then(done)
+});
+```
 
 #### Stubbing
 
-- 
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