ci: Add unit testing infra: (#115)

- Add config for the `jest` unit testing framework.
- Add tests for `utils/math.ts`.
- Add gh-actions workflow to run unit tests.

.github/workflows/test.yaml

@@ -0,0 +1,33 @@
+name: "test"
+
+on:
+  pull_request:
+    types: ["opened", "reopened", "synchronize"]
+  push:
+  schedule:
+    # Run daily at 00:15 UTC (the 15 is to avoid periods of high load)
+    - cron: "15 0 * * *"
+  workflow_dispatch:
+
+permissions: {}
+
+concurrency:
+  group: "${{github.workflow}}-${{github.ref}}"
+
+  # Cancel in-progress jobs for efficiency
+  cancel-in-progress: true
+
+jobs:
+  test:
+    runs-on: "ubuntu-latest"
+    steps:
+      - uses: "actions/checkout@v4"
+        with:
+          submodules: "recursive"
+      - uses: "actions/setup-node@v4"
+        with:
+          node-version: "22"
+          cache: "npm"
+          cache-dependency-path: "./package-lock.json"
+      - run: "npm clean-install"
+      - run: "npm run test"

jest.config.ts

@@ -0,0 +1,71 @@
+import type {Config} from "jest";
+import os from "node:os";
+import pathPosix from "node:path/posix";
+
+
+let PRIMARY_REPORTER: string | [string, Record<string, unknown>] = "default";
+if ("undefined" !== typeof process.env.GITHUB_ACTIONS) {
+    PRIMARY_REPORTER = [
+        "github-actions",
+        {silent: false},
+    ];
+}
+console.log(`Environment variable "GITHUB_ACTIONS"="${process.env.GITHUB_ACTIONS}": ` +
+    `primary reporter will be "${JSON.stringify(PRIMARY_REPORTER)}".`);
+
+const JEST_CONFIG: Config = {
+    collectCoverage: true,
+    collectCoverageFrom: ["src/**/*.{ts,tsx}"],
+    coverageProvider: "v8",
+    coverageReporters: ["text"],
+    coverageThreshold: {
+        "global": {
+            branches: 100,
+            functions: 100,
+            lines: 100,
+        },
+        // eslint-disable-next-line no-warning-comments
+        // TODO: Remove/adjust the overrides below as more test cases are added.
+        "src/": {
+            branches: 0,
+            functions: 0,
+            lines: 0,
+        },
+        "src/utils/math.ts": {
+            branches: 100,
+            functions: 100,
+            lines: 100,
+        },
+    },
+    displayName: {
+        name: "yscope-log-viewer",
+        color: "blue",
+    },
+    errorOnDeprecated: true,
+    maxConcurrency: os.cpus().length,
+    maxWorkers: "100%",
+    openHandlesTimeout: 1000,
+    reporters: [
+        PRIMARY_REPORTER,
+        "summary",
+    ],
+    showSeed: true,
+    testMatch: [
+        pathPosix.join(__dirname, "test/**/?(*)test.{ts,tsx}"),
+    ],
+    testTimeout: 5000,
+    transform: {
+        ".(ts|tsx)$": [
+            "ts-jest",
+            {useESM: true},
+        ],
+    },
+    verbose: true,
+
+    // NOTE: Extra properties in types such as `Error`, `Map`, or `Set` are not preserved when
+    // passing payloads between parent and child threads due to serialization.
+    // See https://jestjs.io/docs/29.6/configuration#workerthreads
+    workerThreads: true,
+};
+
+export default JEST_CONFIG;