feat: create no-conditional-in-test rule (#1027)

Author: G-Rath

README.md

@@ -158,6 +158,7 @@ installations requiring long-term consistency.
 | [no-alias-methods](docs/rules/no-alias-methods.md)                           | Disallow alias methods                                              | ![style][]       | ![fixable][] |
 | [no-commented-out-tests](docs/rules/no-commented-out-tests.md)               | Disallow commented out tests                                        | ![recommended][] |              |
 | [no-conditional-expect](docs/rules/no-conditional-expect.md)                 | Prevent calling `expect` conditionally                              | ![recommended][] |              |
+| [no-conditional-in-test](docs/rules/no-conditional-in-test.md)               | Disallow conditional logic in tests                                 |                  |              |
 | [no-deprecated-functions](docs/rules/no-deprecated-functions.md)             | Disallow use of deprecated functions                                | ![recommended][] | ![fixable][] |
 | [no-disabled-tests](docs/rules/no-disabled-tests.md)                         | Disallow disabled tests                                             | ![recommended][] |              |
 | [no-done-callback](docs/rules/no-done-callback.md)                           | Avoid using a callback in asynchronous tests and hooks              | ![recommended][] | ![suggest][] |

docs/rules/no-conditional-in-test.md

@@ -0,0 +1,79 @@
+# Disallow conditional logic in tests (`no-conditional-in-test`)
+
+Conditional logic in tests is usually an indication that a test is attempting to
+cover too much, and not testing the logic it intends to. Each branch of code
+executing within a conditional statement will usually be better served by a test
+devoted to it.
+
+## Rule Details
+
+This rule reports on any use of a conditional statement such as `if`, `switch`,
+and ternary expressions.
+
+Examples of **incorrect** code for this rule:
+
+```js
+it('foo', () => {
+  if (true) {
+    doTheThing();
+  }
+});
+
+it('bar', () => {
+  switch (mode) {
+    case 'none':
+      generateNone();
+    case 'single':
+      generateOne();
+    case 'multiple':
+      generateMany();
+  }
+
+  expect(fixtures.length).toBeGreaterThan(-1);
+});
+
+it('baz', async () => {
+  const promiseValue = () => {
+    return something instanceof Promise
+      ? something
+      : Promise.resolve(something);
+  };
+
+  await expect(promiseValue()).resolves.toBe(1);
+});
+```
+
+Examples of **correct** code for this rule:
+
+```js
+describe('my tests', () => {
+  if (true) {
+    it('foo', () => {
+      doTheThing();
+    });
+  }
+});
+
+beforeEach(() => {
+  switch (mode) {
+    case 'none':
+      generateNone();
+    case 'single':
+      generateOne();
+    case 'multiple':
+      generateMany();
+  }
+});
+
+it('bar', () => {
+  expect(fixtures.length).toBeGreaterThan(-1);
+});
+
+const promiseValue = something => {
+  return something instanceof Promise ? something : Promise.resolve(something);
+};
+
+it('baz', async () => {
+  await expect(promiseValue()).resolves.toBe(1);
+});
+```

src/__tests__/__snapshots__/rules.test.ts.snap

@@ -16,6 +16,7 @@ Object {
       "jest/no-alias-methods": "error",
       "jest/no-commented-out-tests": "error",
       "jest/no-conditional-expect": "error",
+      "jest/no-conditional-in-test": "error",
       "jest/no-deprecated-functions": "error",
       "jest/no-disabled-tests": "error",
       "jest/no-done-callback": "error",

src/__tests__/rules.test.ts

@@ -2,7 +2,7 @@ import { existsSync } from 'fs';
 import { resolve } from 'path';
 import plugin from '../';
 
-const numberOfRules = 45;
+const numberOfRules = 46;
 const ruleNames = Object.keys(plugin.rules);
 const deprecatedRules = Object.entries(plugin.rules)
   .filter(([, rule]) => rule.meta.deprecated)