Add Jest linting - Add lint to remind you not to leave in an exclusive/focused test

README.md

@@ -12,9 +12,10 @@ This package contains several main ESLint configs for different project styles:
 - `matrix-org/typescript`: The style for TypeScript projects. It extends
   `matrix-org/javascript`.
 
-There is also a mixin config that can be used together with any of the above:
+There are also some mixin configs that can be used together with any of the above:
 
 - `matrix-org/react`: The style for React projects.
+- `matrix-org/jest`: The style for projects that use Jest for testing.
 
 # Getting started
 
@@ -101,7 +102,7 @@ Standard TypeScript with React
 }
 ```
 
-Standard TypeScript with React and jsx a11y
+Standard TypeScript with React, jsx a11y, and Jest
 ```js
 {
     plugins: [
@@ -111,6 +112,7 @@ Standard TypeScript with React and jsx a11y
         "plugin:matrix-org/typescript",
         "plugin:matrix-org/react",
         "plugin:matrix-org/a11y"
+        "plugin:matrix-org/jest"
     ]
 }
 ```
@@ -145,6 +147,7 @@ following depending on the configs you enable:
 * eslint-config-google
 * eslint-config-prettier
 * eslint-plugin-deprecate
+* eslint-plugin-jest
 * eslint-plugin-jsx-a11y
 * eslint-plugin-react
 * eslint-plugin-react-hooks

index.js

@@ -8,5 +8,6 @@ module.exports = {
         "react": require("./react"),
         "typescript": require("./typescript"),
         "a11y": require("./a11y"),
+        "jest": require("./jest"),
     },
 };

jest.js

@@ -0,0 +1,20 @@
+module.exports = {
+    plugins: ["jest"],
+    extends: ["plugin:jest/recommended"],
+    rules: {
+        "jest/no-standalone-expect": [
+            "error",
+            {
+                additionalTestBlockFunctions: [
+                    // Tested and assertions in `before`/`beforeEach` blocks will fail
+                    // the test as expected
+                    "before",
+                    "beforeEach",
+                ],
+            },
+        ],
+        // It's ok to have no expect assertions in your test. Maybe you're testing that
+        // things just don't blow up.
+        "jest/expect-expect": "off",
+    },
+};

package.json

@@ -26,6 +26,7 @@
         "eslint-config-prettier": "*",
         "eslint-plugin-deprecate": "*",
         "eslint-plugin-import": "*",
+        "eslint-plugin-jest": "*",
         "eslint-plugin-jsx-a11y": "*",
         "eslint-plugin-react": "*",
         "eslint-plugin-react-hooks": "*",