feat(rules): no-duplicate-hooks (#298)

Fixes #231

README.md

@@ -112,6 +112,7 @@ installations requiring long-term consistency.
 | [no-alias-methods][]         | Disallow alias methods                                            | ![recommended][] | ![fixable-green][]  |
 | [no-disabled-tests][]        | Disallow disabled tests                                           | ![recommended][] |                     |
 | [no-commented-out-tests][]   | Disallow commented out tests                                      |                  |                     |
+| [no-duplicate-hooks][]       | Disallow duplicate hooks withing a `describe` block               |                  |                     |
 | [no-empty-title][]           | Disallow empty titles                                             |                  |                     |
 | [no-focused-tests][]         | Disallow focused tests                                            | ![recommended][] |                     |
 | [no-hooks][]                 | Disallow setup and teardown hooks                                 |                  |                     |
@@ -158,6 +159,7 @@ https://github.com/dangreenisrael/eslint-plugin-jest-formatting
 [lowercase-name]: docs/rules/lowercase-name.md
 [no-alias-methods]: docs/rules/no-alias-methods.md
 [no-disabled-tests]: docs/rules/no-disabled-tests.md
+[no-duplicate-hooks]: docs/rules/no-duplicate-hooks.md
 [no-commented-out-tests]: docs/rules/no-commented-out-tests.md
 [no-empty-title]: docs/rules/no-empty-title.md
 [no-focused-tests]: docs/rules/no-focused-tests.md

docs/rules/no-duplicate-hooks.md

@@ -0,0 +1,75 @@
+# Disallow duplicate setup and teardown hooks (no-duplicate-hooks)
+
+A describe block should not contain duplicate hooks.
+
+## Rule Details
+
+Examples of **incorrect** code for this rule
+
+```js
+/* eslint jest/no-duplicate-hooks: "error" */
+
+describe('foo', () => {
+  beforeEach(() => {
+    // some setup
+  });
+  beforeEach(() => {
+    // some setup
+  });
+  test('foo_test', () => {
+    // some test
+  });
+});
+
+// Nested describe scenario
+describe('foo', () => {
+  beforeEach(() => {
+    // some setup
+  });
+  test('foo_test', () => {
+    // some test
+  });
+  describe('bar', () => {
+    test('bar_test', () => {
+      afterAll(() => {
+        // some teardown
+      });
+      afterAll(() => {
+        // some teardown
+      });
+    });
+  });
+});
+```
+
+Examples of **correct** code for this rule
+
+```js
+/* eslint jest/no-duplicate-hooks: "error" */
+
+describe('foo', () => {
+  beforeEach(() => {
+    // some setup
+  });
+  test('foo_test', () => {
+    // some test
+  });
+});
+
+// Nested describe scenario
+describe('foo', () => {
+  beforeEach(() => {
+    // some setup
+  });
+  test('foo_test', () => {
+    // some test
+  });
+  describe('bar', () => {
+    test('bar_test', () => {
+      beforeEach(() => {
+        // some setup
+      });
+    });
+  });
+});
+```

src/__tests__/rules.test.js

@@ -5,7 +5,7 @@ const path = require('path');
 const { rules } = require('../');
 
 const ruleNames = Object.keys(rules);
-const numberOfRules = 32;
+const numberOfRules = 33;
 
 describe('rules', () => {
   it('should have a corresponding doc for each rule', () => {