test: install and setup jest (#9)

* test: install and setup jest

* test: install eslint-plugin-jest

eslint.config.mjs

@@ -1,13 +1,17 @@
 // @ts-check
 
+// apparently it's not standard to publish types for eslint plugins
+
 import pluginJs from "@eslint/js";
-// @ts-expect-error couldn't find types for this package
+// @ts-expect-error no types for this plugin
 import pluginBetterMutation from "eslint-plugin-better-mutation";
-// @ts-expect-error couldn't find types for this package
+// @ts-expect-error no types for this plugin
+import pluginJest from "eslint-plugin-jest";
+// @ts-expect-error no types for this plugin
 import pluginJsxA11y from "eslint-plugin-jsx-a11y";
-// @ts-expect-error couldn't find types for this package
+// @ts-expect-error no types for this plugin
 import pluginReactHooks from "eslint-plugin-react-hooks";
-// @ts-expect-error couldn't find types for this package
+// @ts-expect-error no types for this plugin
 import pluginReactConfig from "eslint-plugin-react/configs/jsx-runtime.js";
 import globals from "globals";
 import tseslint from "typescript-eslint";
@@ -66,7 +70,12 @@ export default tseslint.config(
   },
   {
     files: ["js/test/", "js/**/*.test.*"],
+    // we use both jest's recommended and style rules, but only need to set the plugin once here,
+    // and it doesn't matter which config we get the plugin from.
+    ...pluginJest.configs["flat/recommended"],
     rules: {
+      ...pluginJest.configs["flat/style"].rules,
+      ...pluginJest.configs["flat/recommended"].rules,
       // empty functions are fine
       "@typescript-eslint/no-empty-function": "off",
       // expect.any is untyped and triggers this all the time.

jest.config.ts

@@ -0,0 +1,207 @@
+/**
+ * For a detailed explanation regarding each configuration property, visit:
+ * https://jestjs.io/docs/configuration
+ */
+
+//import type {Config} from 'jest';
+import type { JestConfigWithTsJest } from "ts-jest";
+
+const config: JestConfigWithTsJest = {
+  // All imported modules in your tests should be mocked automatically
+  // automock: false,
+
+  // Stop running tests after `n` failures
+  // bail: 0,
+
+  // The directory where Jest should store its cached dependency information
+  // cacheDirectory: "/private/var/folders/_c/pkbh9ch11vb854mvz5phx814nxfrl6/T/jest_c5x2zq",
+
+  // Automatically clear mock calls, instances, contexts and results before every test
+  clearMocks: true,
+
+  // Indicates whether the coverage information should be collected while executing the test
+  // collectCoverage: false,
+
+  // An array of glob patterns indicating a set of files for which coverage information should be collected
+  // collectCoverageFrom: undefined,
+
+  // The directory where Jest should output its coverage files
+  // coverageDirectory: undefined,
+
+  // An array of regexp pattern strings used to skip coverage collection
+  // coveragePathIgnorePatterns: [
+  //   "/node_modules/"
+  // ],
+
+  // Indicates which provider should be used to instrument code for coverage
+  // coverageProvider: "v8",
+
+  // A list of reporter names that Jest uses when writing coverage reports
+  // coverageReporters: [
+  //   "json",
+  //   "text",
+  //   "lcov",
+  //   "clover"
+  // ],
+
+  // An object that configures minimum threshold enforcement for coverage results
+  // coverageThreshold: undefined,
+
+  // A path to a custom dependency extractor
+  // dependencyExtractor: undefined,
+
+  // Make calling deprecated APIs throw helpful error messages
+  // errorOnDeprecated: false,
+
+  // The default configuration for fake timers
+  // fakeTimers: {
+  //   "enableGlobally": false
+  // },
+
+  // Force coverage collection from ignored files using an array of glob patterns
+  // forceCoverageMatch: [],
+
+  // A path to a module which exports an async function that is triggered once before all test suites
+  // globalSetup: undefined,
+
+  // A path to a module which exports an async function that is triggered once after all test suites
+  // globalTeardown: undefined,
+
+  // A set of global variables that need to be available in all test environments
+  // globals: {},
+
+  // The maximum amount of workers used to run your tests. Can be specified as % or a number. E.g. maxWorkers: 10% will use 10% of your CPU amount + 1 as the maximum worker number. maxWorkers: 2 will use a maximum of 2 workers.
+  // maxWorkers: "50%",
+
+  // An array of directory names to be searched recursively up from the requiring module's location
+  // moduleDirectories: [
+  //   "node_modules"
+  // ],
+
+  // An array of file extensions your modules use
+  // moduleFileExtensions: [
+  //   "js",
+  //   "mjs",
+  //   "cjs",
+  //   "jsx",
+  //   "ts",
+  //   "tsx",
+  //   "json",
+  //   "node"
+  // ],
+
+  // A map from regular expressions to module names or to arrays of module names that allow to stub out resources with a single module
+  // moduleNameMapper: {},
+
+  // An array of regexp pattern strings, matched against all module paths before considered 'visible' to the module loader
+  // modulePathIgnorePatterns: [],
+
+  // Activates notifications for test results
+  // notify: false,
+
+  // An enum that specifies notification mode. Requires { notify: true }
+  // notifyMode: "failure-change",
+
+  // A preset that is used as a base for Jest's configuration
+  preset: "ts-jest",
+
+  // Run tests from one or more projects
+  // projects: undefined,
+
+  // Use this configuration option to add custom reporters to Jest
+  // reporters: undefined,
+
+  // Automatically reset mock state before every test
+  // resetMocks: false,
+
+  // Reset the module registry before running each individual test
+  // resetModules: false,
+
+  // A path to a custom resolver
+  // resolver: undefined,
+
+  // Automatically restore mock state and implementation before every test
+  // restoreMocks: false,
+
+  // The root directory that Jest should scan for tests and modules within
+  // rootDir: undefined,
+
+  // A list of paths to directories that Jest should use to search for files in
+  // roots: [
+  //   "<rootDir>"
+  // ],
+
+  // Allows you to use a custom runner instead of Jest's default test runner
+  // runner: "jest-runner",
+
+  // The paths to modules that run some code to configure or set up the testing environment before each test
+  // setupFiles: [],
+
+  // A list of paths to modules that run some code to configure or set up the testing framework before each test
+  setupFilesAfterEnv: ["<rootDir>/js/test/setupTest.ts"],
+
+  // The number of seconds after which a test is considered as slow and reported as such in the results.
+  // slowTestThreshold: 5,
+
+  // A list of paths to snapshot serializer modules Jest should use for snapshot testing
+  // snapshotSerializers: [],
+
+  // The test environment that will be used for testing
+  testEnvironment: "jsdom",
+
+  // Options that will be passed to the testEnvironment
+  // testEnvironmentOptions: {},
+
+  // Adds a location field to test results
+  // testLocationInResults: false,
+
+  // The glob patterns Jest uses to detect test files
+  // testMatch: [
+  //   "**/__tests__/**/*.[jt]s?(x)",
+  //   "**/?(*.)+(spec|test).[tj]s?(x)"
+  // ],
+
+  // An array of regexp pattern strings that are matched against all test paths, matched tests are skipped
+  // testPathIgnorePatterns: [
+  //   "/node_modules/"
+  // ],
+
+  // The regexp pattern or array of patterns that Jest uses to detect test files
+  // testRegex: [],
+
+  // This option allows the use of a custom results processor
+  // testResultsProcessor: undefined,
+
+  // This option allows use of a custom test runner
+  // testRunner: "jest-circus/runner",
+
+  // A map from regular expressions to paths to transformers
+  transform: {
+    "^.+\\.tsx?$": [
+      "ts-jest",
+      {
+        // ts-jest configuration goes here
+      },
+    ],
+  },
+
+  // An array of regexp pattern strings that are matched against all source file paths, matched files will skip transformation
+  // transformIgnorePatterns: [
+  //   "/node_modules/",
+  //   "\\.pnp\\.[^\\/]+$"
+  // ],
+
+  // An array of regexp pattern strings that are matched against all modules before the module loader will automatically return a mock for them
+  // unmockedModulePathPatterns: undefined,
+
+  // Indicates whether each individual test should be reported during the run
+  // verbose: undefined,
+
+  // An array of regexp patterns that are matched against all source file paths before re-running tests in watch mode
+  // watchPathIgnorePatterns: [],
+
+  // Whether to use watchman for file crawling
+  // watchman: true,
+};
+
+export default config;

js/helloWorld.test.ts

@@ -0,0 +1,15 @@
+/**
+ * This is a placeholder test to show that jest is set up and working
+ * It can be removed once we have our first real functionality to test
+ * (which will probably be a basic render(<App/>) test when we set up React)
+ */
+
+import { onePlusOne } from "./helloWorld";
+
+describe("onePlusOne", () => {
+  test("can run a test", () => {
+    // using toBeOneOf shows that jest-extended-matchers is working
+    // and therefore that the setup script is being called
+    expect(onePlusOne()).toBeOneOf([1, 2, 3]);
+  });
+});

js/helloWorld.ts

@@ -0,0 +1,7 @@
+/**
+ * This is a placeholder to show that jest is set up and working
+ * It can be removed once we have our first real functionality to test
+ * (which will probably be a the react <App/>)
+ */
+
+export const onePlusOne = () => 2;

js/test/setupTest.ts

@@ -0,0 +1,5 @@
+import "@testing-library/jest-dom";
+// add all jest-extended matchers
+import * as jestExtendedMatchers from "jest-extended";
+
+expect.extend(jestExtendedMatchers);