Introduce a lint rule to report error when testing promises. If a exp…

README.md

@@ -89,6 +89,7 @@ for more information about extending configuration files.
 | [prefer-to-be-undefined](docs/rules/prefer-to-be-undefined.md)     | Suggest using `toBeUndefined()`                                 |                                                                         | ![fixable](https://img.shields.io/badge/-fixable-green.svg) |
 | [prefer-expect-assertions](docs/rules/prefer-expect-assertions.md) | Suggest using `expect.assertions()` OR `expect.hasAssertions()` |                                                                         |                                                             |
 | [valid-expect](docs/rules/valid-expect.md)                         | Enforce valid `expect()` usage                                  | ![recommended](https://img.shields.io/badge/-recommended-lightgrey.svg) |                                                             |
+| [valid-expect-in-promise](docs/rules/valid-expect-in-promise.md)   | Enforce having return statement when testing with promises      |                                                                         |                                                             |
 
 ## Credit
 

docs/rules/valid-expect-in-promise.md

@@ -0,0 +1,33 @@
+# Enforce having return statement when testing with promises (valid-expect-in-promise)
+
+Ensure to return promise when having assertions in `then` or `catch` block of
+promise
+
+## Rule details
+
+This rule triggers a warning if,
+
+* test is having assertions in `then` or `catch` block of a promise
+* and that promise is not returned from the test
+
+### Default configuration
+
+The following pattern is considered warning:
+
+```js
+it('promise test', () => {
+  somePromise.then(data => {
+    expect(data).toEqual('foo');
+  });
+});
+```
+
+The following pattern is not warning:
+
+```js
+it('promise test', () => {
+  return somePromise.then(data => {
+    expect(data).toEqual('foo');
+  });
+});
+```

index.js

@@ -9,6 +9,7 @@ const preferToBeUndefined = require('./rules/prefer_to_be_undefined');
 const preferToHaveLength = require('./rules/prefer_to_have_length');
 const validExpect = require('./rules/valid_expect');
 const preferExpectAssertions = require('./rules/prefer_expect_assertions');
+const validExpectInPromise = require('./rules/valid_expect_in_promise');
 
 const snapshotProcessor = require('./processors/snapshot-processor');
 
@@ -64,5 +65,6 @@ module.exports = {
     'prefer-to-have-length': preferToHaveLength,
     'valid-expect': validExpect,
     'prefer-expect-assertions': preferExpectAssertions,
+    'valid-expect-in-promise': validExpectInPromise,
   },
 };