feat: create new no-unnecessary-assertion rule (#1882)

* feat: create new `no-unnecessary-assertion` rule

* feat: support "undefined" matchers too

* test: add some more cases

* docs: add doc for rule

* fix: mark rule as requiring typechecking

* fix: only import TypeScript at runtime if rule is enabled

* test: disable automatic single run inference

* fix: error if strict null checks is not enabled

* test: ensure that we don't require typescript

* perf: load typescript after we know strict null checks is enabled

Author: G-Rath

README.md

@@ -394,9 +394,10 @@ Manually fixable by
 
 ### Requires Type Checking
 
-| Name                                           | Description                                                  | 💼  | ⚠️  | 🔧  | 💡  |
-| :--------------------------------------------- | :----------------------------------------------------------- | :-- | :-- | :-- | :-- |
-| [unbound-method](docs/rules/unbound-method.md) | Enforce unbound methods are called with their expected scope |     |     |     |     |
+| Name                                                               | Description                                                  | 💼  | ⚠️  | 🔧  | 💡  |
+| :----------------------------------------------------------------- | :----------------------------------------------------------- | :-- | :-- | :-- | :-- |
+| [no-unnecessary-assertion](docs/rules/no-unnecessary-assertion.md) | Disallow unnecessary assertions based on types               |     |     |     |     |
+| [unbound-method](docs/rules/unbound-method.md)                     | Enforce unbound methods are called with their expected scope |     |     |     |     |
 
 <!-- end auto-generated rules list -->
 

docs/rules/no-unnecessary-assertion.md

@@ -0,0 +1,35 @@
+# Disallow unnecessary assertions based on types (`no-unnecessary-assertion`)
+
+💭 This rule requires
+[type information](https://typescript-eslint.io/linting/typed-linting).
+
+<!-- end auto-generated rule header -->
+
+When using TypeScript, runtime assertions based on types can often be omitted
+provided that the types are accurate.
+
+## Rule details
+
+This rule warns when you do an assertion about being `null` or `undefined` on
+something that cannot be those types, as that indicates either the assertion can
+be removed or the types need to be adjusted.
+
+The following patterns are considered warnings:
+
+```ts
+expect('hello world'.match('sunshine') ?? []).toBeNull();
+
+expect(User.findOrThrow(1)).toBeDefined();
+
+expect(map.getOrInsert('key', 'default')).not.toBeUndefined();
+```
+
+The following patterns are not considered warnings:
+
+```ts
+expect('hello world'.match('sunshine')).toBeNull();
+
+expect(User.findOrNull(1)).toBeDefined();
+
+expect(map.get('key')).not.toBeUndefined();
+```

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

@@ -36,6 +36,7 @@ exports[`rules should export configs that refer to actual rules 1`] = `
       "jest/no-standalone-expect": "error",
       "jest/no-test-prefixes": "error",
       "jest/no-test-return-statement": "error",
+      "jest/no-unnecessary-assertion": "error",
       "jest/no-unneeded-async-expect-function": "error",
       "jest/no-untyped-mock-factory": "error",
       "jest/padding-around-after-all-blocks": "error",
@@ -132,6 +133,7 @@ exports[`rules should export configs that refer to actual rules 1`] = `
       "jest/no-standalone-expect": "error",
       "jest/no-test-prefixes": "error",
       "jest/no-test-return-statement": "error",
+      "jest/no-unnecessary-assertion": "error",
       "jest/no-unneeded-async-expect-function": "error",
       "jest/no-untyped-mock-factory": "error",
       "jest/padding-around-after-all-blocks": "error",

src/__tests__/rules.test.ts

@@ -2,7 +2,7 @@ import { existsSync } from 'fs';
 import { resolve } from 'path';
 import plugin from '../';
 
-const numberOfRules = 67;
+const numberOfRules = 68;
 const ruleNames = Object.keys(plugin.rules);
 const deprecatedRules = Object.entries(plugin.rules)
   .filter(([, rule]) => rule.meta.deprecated)