writing-bundler-tests

```typescript

import { describe } from "bun:test";

import { itBundled, dedent } from "./expectBundled";

describe("bundler", () => {

itBundled("category/TestName", {

files: {

"index.js": console.log("hello");,

},

run: {

stdout: "hello",

},

});

});

```

Test ID format: category/TestName (e.g., banner/CommentBanner, minify/Empty)

```typescript

{

files: {

"index.js": console.log("test");,

"lib.ts": export const foo = 123;,

"nested/file.js": export default {};,

},

entryPoints: ["index.js"], // defaults to first file

runtimeFiles: { // written AFTER bundling

"extra.js": console.log("added later");,

},

}

```

```typescript

{

outfile: "/out.js",

outdir: "/out",

format: "esm" | "cjs" | "iife",

target: "bun" | "browser" | "node",

// Minification

minifyWhitespace: true,

minifyIdentifiers: true,

minifySyntax: true,

// Code manipulation

banner: "// copyright",

footer: "// end",

define: { "PROD": "true" },

external: ["lodash"],

// Advanced

sourceMap: "inline" | "external",

splitting: true,

treeShaking: true,

drop: ["console"],

}

```

```typescript

{

run: {

stdout: "expected output", // exact match

stdout: /regex/, // pattern match

partialStdout: "contains this", // substring

stderr: "error output",

exitCode: 1,

env: { NODE_ENV: "production" },

runtime: "bun" | "node",

// Runtime errors

error: "ReferenceError: x is not defined",

},

}

```

```typescript

{

bundleErrors: {

"/file.js": ["error message 1", "error message 2"],

},

bundleWarnings: {

"/file.js": ["warning message"],

},

}

```

Add markers in source code:

```javascript

// KEEP - this should survive

const used = 1;

// REMOVE - this should be eliminated

const unused = 2;

```

```typescript

{

dce: true,

dceKeepMarkerCount: 5, // expected KEEP markers

}

```

Verify exact transpilation with capture():

```typescript

itBundled("string/Folding", {

files: {

"index.ts": capture(\\${1 + 1}\);,

},

capture: ['"2"'], // expected captured value

minifySyntax: true,

});

```

```typescript

{

onAfterBundle(api) {

api.expectFile("out.js").toContain("console.log");

api.assertFileExists("out.js");

const content = api.readFile("out.js");

expect(content).toMatchSnapshot();

const values = api.captureFile("out.js");

expect(values).toEqual(["2"]);

},

}

```

Simple output verification:

```typescript

itBundled("banner/Comment", {

banner: "// copyright",

files: { "a.js": console.log("Hello") },

onAfterBundle(api) {

api.expectFile("out.js").toContain("// copyright");

},

});

```

Multi-file CJS/ESM interop:

```typescript

itBundled("cjs/ImportSyntax", {

files: {

"entry.js": import lib from './lib.cjs'; console.log(lib);,

"lib.cjs": exports.foo = 'bar';,

},

run: { stdout: '{"foo":"bar"}' },

});

```

Error handling:

```typescript

itBundled("edgecase/InvalidLoader", {

files: { "index.js": ... },

bundleErrors: {

"index.js": ["Unsupported loader type"],

},

});

```

```text

test/bundler/

├── bundler_banner.test.ts

├── bundler_string.test.ts

├── bundler_minify.test.ts

├── bundler_cjs.test.ts

├── bundler_edgecase.test.ts

├── bundler_splitting.test.ts

├── css/

├── transpiler/

└── expectBundled.ts

```

```bash

bun bd test test/bundler/bundler_banner.test.ts

BUN_BUNDLER_TEST_FILTER="banner/Comment" bun bd test bundler_banner.test.ts

BUN_BUNDLER_TEST_DEBUG=1 bun bd test bundler_minify.test.ts

```

• Use dedent for readable multi-line code
• File paths are relative (e.g., /index.js)
• Use capture() to verify exact transpilation results
• Use .toMatchSnapshot() for complex outputs
• Pass array to run for multiple test scenarios