chore: added preliminary internal unit tests

.github/workflows/test.yml

@@ -0,0 +1,15 @@
+name: Format
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+jobs:
+  format:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: ./.github/actions/prepare
+      - run: yarn test

.vscode/launch.json

@@ -0,0 +1,16 @@
+{
+  "configurations": [
+    {
+      "args": ["run", "${relativeFile}"],
+      "autoAttachChildProcesses": true,
+      "console": "integratedTerminal",
+      "name": "Debug Current Test File",
+      "program": "${workspaceRoot}/node_modules/vitest/vitest.mjs",
+      "request": "launch",
+      "skipFiles": ["<node_internals>/**", "**/node_modules/**"],
+      "smartStep": true,
+      "type": "node"
+    }
+  ],
+  "version": "0.2.0"
+}

docs/Development.md

@@ -81,3 +81,19 @@ The function should return an object with:
 - `restore`: Restores the original method on the container.
 
 See [`src/spies/jest.ts`](../src/spies/jest.ts) as an example.
+
+## Unit Tests
+
+This repository uses [Vitest](https://vitest.dev) for a small amount of unit test coverage.
+You can run it locally on the command-line:
+
+```shell
+pnpm run test
+```
+
+Test environments and spy frameworks don't need to be unit tested just yet.
+
+### Debugging Tests
+
+This repository includes a [VS Code launch configuration](https://code.visualstudio.com/docs/editor/debugging) for debugging unit tests.
+To launch it, open a test file, then run _Debug Current Test File_ from the VS Code Debug panel (or press F5).

package.json

@@ -14,7 +14,8 @@
     "npm-run-all": "^4.1.5",
     "prettier": "^2.7.1",
     "pretty-quick": "^3.1.3",
-    "typescript": "^4.7.4"
+    "typescript": "^4.7.4",
+    "vitest": "^0.31.0"
   },
   "main": "src/index.js",
   "husky": {
@@ -43,7 +44,8 @@
     "lint": "yarn eslint \"src/*.ts\"  --max-warnings 0 --report-unused-disable-directives",
     "lint:md": "yarn markdownlint \"**/*.md\" \".github/**/*.md\"",
     "lint:spelling": "cspell \"**\" \".github/**/*\"",
-    "prepare": "husky install"
+    "prepare": "husky install",
+    "test": "vitest"
   },
   "version": "0.2.1"
 }

src/complaining/createComplaint.ts

@@ -0,0 +1,24 @@
+import { TestComplaint } from "../environments/testEnvironmentTypes";
+import { SpyCallArgs } from "../spies/spyTypes";
+import { formatMethodComplaint } from "./formatMethodComplaint";
+
+export const createComplaint = (
+  methodsWithCalls: [keyof Console, SpyCallArgs[]][],
+): TestComplaint => {
+  const methodComplaints = methodsWithCalls.map(formatMethodComplaint).join("\n");
+  const s = methodsWithCalls.length === 1 ? "" : "s";
+
+  // It looks like something wrote to the console during your test!
+  // Put a breakpoint on this line and check the methodsWithCalls variable to see details.
+  const error = new Error(
+    `Oh no! Your test called the following console method${s}:\n${methodComplaints}`,
+  );
+
+  return {
+    error,
+    methodComplaints: methodsWithCalls.map(([methodName, methodCalls]) => ({
+      methodCalls,
+      methodName,
+    })),
+  };
+};

src/complaining/formatComplaintCall.test.ts

@@ -0,0 +1,16 @@
+import { describe, expect, it } from "vitest";
+import { formatComplaintCall } from "./formatComplaintCall";
+
+describe("formatComplaintCall", () => {
+  it.each([
+    [[false], "false"],
+    [[true], "true"],
+    [[{}], "{}"],
+    [[{ inner: {} }], '{"inner":{}}'],
+    [[1, "two", [3]], '1, "two", [3]'],
+  ])(`formats %p as %p`, (args, expected) => {
+    const actual = formatComplaintCall(args);
+
+    expect(actual).toBe(expected);
+  });
+});

src/complaining/formatComplaintCall.ts

@@ -0,0 +1,8 @@
+import { SpyCallArgs } from "../spies/spyTypes";
+
+const formatComplaintLineArg = (arg: unknown) => {
+  return JSON.stringify(arg) || JSON.stringify(`${arg}`);
+};
+
+export const formatComplaintCall = (call: SpyCallArgs) =>
+  call.map(formatComplaintLineArg).join(", ");

src/complaining/formatMethodComplaint.ts

@@ -0,0 +1,21 @@
+import { SpyCallArgs } from "../spies/spyTypes";
+import { formatComplaintCall } from "./formatComplaintCall";
+
+const lineThreshold = 3;
+
+export const formatMethodComplaint = ([methodName, calls]: [keyof Console, SpyCallArgs[]]) => {
+  const summary = `  * ${methodName} (${calls.length} call${calls.length === 1 ? "" : "s"})`;
+
+  const lines = calls
+    .slice(0, Math.min(calls.length, lineThreshold))
+    .map(formatComplaintLineWithIndex);
+
+  if (calls.length > lineThreshold) {
+    lines.push(`...${calls.length - lineThreshold} more`);
+  }
+
+  return `${summary}\n${lines.map((line) => `    > Call ${line}`).join("\n")}`;
+};
+
+const formatComplaintLineWithIndex = (call: SpyCallArgs, i: number) =>
+  `${i}: ${formatComplaintCall(call)}`;

src/complaining/index.ts

@@ -0,0 +1,3 @@
+export { createComplaint } from "./createComplaint";
+export { formatComplaintCall } from "./formatComplaintCall";
+export { formatMethodComplaint } from "./formatMethodComplaint";

vitest.config.js

@@ -0,0 +1,9 @@
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+const config_1 = require("vitest/config");
+exports.default = (0, config_1.defineConfig)({
+  test: {
+    clearMocks: true,
+    exclude: ["lib", "node_modules", "src/**/*.js", "src/*/*.js"],
+  },
+});

vitest.config.ts

@@ -0,0 +1,8 @@
+import { defineConfig } from "vitest/config";
+
+export default defineConfig({
+  test: {
+    clearMocks: true,
+    exclude: ["lib", "node_modules", "src/**/*.js", "src/*/*.js"],
+  },
+});