feat: create no-conditional-expect rule

Author: G-Rath

README.md

@@ -134,6 +134,7 @@ installations requiring long-term consistency.
 | [lowercase-name](docs/rules/lowercase-name.md)                         | Enforce lowercase test names                                    |                  | ![fixable][] |
 | [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                          |                  |              |
 | [no-deprecated-functions](docs/rules/no-deprecated-functions.md)       | Disallow use of deprecated functions                            |                  | ![fixable][] |
 | [no-disabled-tests](docs/rules/no-disabled-tests.md)                   | Disallow disabled tests                                         | ![recommended][] |              |
 | [no-duplicate-hooks](docs/rules/no-duplicate-hooks.md)                 | Disallow duplicate setup and teardown hooks                     |                  |              |

docs/rules/no-conditional-expect.md

@@ -0,0 +1,70 @@
+# Prevent calling `expect` conditionally (`no-conditional-expect`)
+
+This rule prevents the use of `expect` in conditional blocks, such as `if`s &
+`catch`s.
+
+## Rule Details
+
+Jest considered a test to have failed if it throws an error, rather than on if
+any particular function is called, meaning conditional calls to `expect` could
+result in tests silently being skipped.
+
+Additionally, conditionals tend to make tests more brittle and complex, as they
+increase the amount of mental thinking needed to understand what is actually
+being tested.
+
+While `expect.assertions` & `expect.hasAssertions` can help prevent tests from
+silently being skipped, when combined with conditionals they typically result in
+even more complexity being introduced.
+
+The following patterns are warnings:
+
+```js
+it('foo', () => {
+  doTest && expect(1).toBe(2);
+});
+
+it('bar', () => {
+  if (!skipTest) {
+    expect(1).toEqual(2);
+  }
+});
+
+it('baz', async () => {
+  try {
+    await foo();
+  } catch (err) {
+    expect(err).toMatchObject({ code: 'MODULE_NOT_FOUND' });
+  }
+});
+```
+
+The following patterns are not warnings:
+
+```js
+it('foo', () => {
+  expect(!value).toBe(false);
+});
+
+function getValue() {
+  if (process.env.FAIL) {
+    return 1;
+  }
+
+  return 2;
+}
+
+it('foo', () => {
+  expect(getValue()).toBe(2);
+});
+
+it('validates the request', () => {
+  try {
+    processRequest(request);
+  } catch {
+    // ignore errors
+  } finally {
+    expect(validRequest).toHaveBeenCalledWith(request);
+  }
+});
+```

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

@@ -15,6 +15,7 @@ Object {
       "jest/lowercase-name": "error",
       "jest/no-alias-methods": "error",
       "jest/no-commented-out-tests": "error",
+      "jest/no-conditional-expect": "error",
       "jest/no-deprecated-functions": "error",
       "jest/no-disabled-tests": "error",
       "jest/no-duplicate-hooks": "error",

src/__tests__/rules.test.ts

@@ -3,7 +3,7 @@ import { resolve } from 'path';
 import plugin from '../';
 
 const ruleNames = Object.keys(plugin.rules);
-const numberOfRules = 42;
+const numberOfRules = 43;
 
 describe('rules', () => {
   it('should have a corresponding doc for each rule', () => {