test: add test case for parsing args correctly

test/fixtures/parse_args/src/a.ts

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+export const a = 'a';
+
+export const a2 = 'a2';

test/fixtures/parse_args/src/main.ts

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+import { a } from '@/a.js';
+
+console.log(a);

test/fixtures/parse_args/tsconfig.json

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+{
+  "compilerOptions": {
+    "paths": {
+      // this can be anything, it's just specified to check if we're reading the tsconfig correctly
+      "@/*": ["./src/*"]
+    }
+  }
+}

test/fixtures/parse_args/tsconfig.main.json

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+{
+  "include": ["src/main.ts"]
+}

test/parse_args.test.ts

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+import assert from 'node:assert/strict';
+import * as child_process from 'node:child_process';
+import { promisify } from 'node:util';
+import { dirname, resolve } from 'node:path';
+import { describe, it } from 'node:test';
+import { fileURLToPath } from 'node:url';
+import stripAnsi from 'strip-ansi';
+
+const exec = promisify(child_process.exec);
+
+const projectRoot = resolve(
+  dirname(fileURLToPath(import.meta.url)),
+  'fixtures/parse_args',
+);
+
+const bin = resolve(dirname(fileURLToPath(import.meta.url)), '../dist/cli.js');
+
+await exec('npm run build', { cwd: projectRoot });
+
+describe('parse_args', () => {
+  it('should show help', async () => {
+    const { stdout } = await exec(`node ${bin} --help`);
+
+    const output = stripAnsi(stdout);
+
+    assert.equal(
+      output,
+      `
+Usage:
+  tsr [options] [...entrypoints]
+
+Options:
+  -p, --project <file>    Path to your tsconfig.json
+  -w, --write             Write changes in place
+  -r, --recursive         Recursively look into files until the project is clean
+  --include-d-ts          Check for unused code in .d.ts files
+  -h, --help              Display this message
+  -v, --version           Display version number
+
+Examples:
+  # Check unused code for a project with an entrypoint of src/main.ts
+  tsr 'src/main\\.ts$'
+
+  # Write changes in place
+  tsr --write 'src/main\\.ts$'
+
+  # Check unused code for a project with a custom tsconfig.json
+  tsr --project tsconfig.app.json 'src/main\\.ts$'
+
+  # Check unused code for a project with multiple entrypoints in src/pages
+  tsr 'src/pages/.*\\.ts$'
+
+`,
+    );
+  });
+
+  it('should use default tsconfig.json', async () => {
+    const { stdout, code } = await exec(`node ${bin} 'src/main\\.ts$'`, {
+      cwd: projectRoot,
+    })
+      .then((res) => ({ ...res, code: 0 }))
+      .catch((e) => e as { stdout: string; code: number });
+
+    const output = stripAnsi(stdout.toString());
+
+    assert.equal(
+      output,
+      `tsconfig tsconfig.json
+Project has 2 files. Found 1 entrypoint file
+export src/a.ts:2:0     'a2'
+✖ remove 1 export
+`,
+    );
+    assert.equal(code, 1);
+  });
+
+  it('should work with custom tsconfig.json', async () => {
+    const { stdout, code } = await exec(
+      `node ${bin} --project tsconfig.main.json 'src/main\\.ts$'`,
+      {
+        cwd: projectRoot,
+      },
+    )
+      .then((res) => ({ ...res, code: 0 }))
+      .catch((e) => e as { stdout: string; code: number });
+
+    const output = stripAnsi(stdout.toString());
+
+    assert.equal(
+      output,
+      `tsconfig tsconfig.main.json
+Project has 1 file. Found 1 entrypoint file
+✔ all good!
+`,
+    );
+    assert.equal(code, 0);
+  });
+});