test: add unit tests for interactive install prompt

Cover the four promptInstall/loadTransformers paths:
- non-TTY skips prompt and exits with error
- TTY + user declines → exits with error
- TTY + user accepts but npm install fails → exits with error
- TTY + install succeeds → retries import and loads module

Author: github-actions[bot]

tests/unit/prompt-install.test.js

@@ -0,0 +1,138 @@
+/**
+ * Unit tests for the interactive install prompt in src/embedder.js.
+ *
+ * Tests the promptInstall() + loadTransformers() flow when
+ * @huggingface/transformers is missing.
+ *
+ * Each test uses vi.resetModules() + vi.doMock() + dynamic import()
+ * so every test gets a fresh embedder module with its own mocks.
+ */
+
+import { afterEach, beforeEach, describe, expect, test, vi } from 'vitest';
+
+describe('loadTransformers install prompt', () => {
+  let exitSpy;
+  let errorSpy;
+  let logSpy;
+  let origTTY;
+
+  beforeEach(() => {
+    vi.resetModules();
+    origTTY = process.stdin.isTTY;
+    exitSpy = vi.spyOn(process, 'exit').mockImplementation((code) => {
+      throw new Error(`process.exit(${code})`);
+    });
+    errorSpy = vi.spyOn(console, 'error').mockImplementation(() => {});
+    logSpy = vi.spyOn(console, 'log').mockImplementation(() => {});
+  });
+
+  afterEach(() => {
+    process.stdin.isTTY = origTTY;
+    exitSpy.mockRestore();
+    errorSpy.mockRestore();
+    logSpy.mockRestore();
+    vi.restoreAllMocks();
+  });
+
+  test('non-TTY: prints error and exits without prompting', async () => {
+    process.stdin.isTTY = undefined;
+
+    const rlFactory = vi.fn();
+    vi.doMock('node:readline', () => ({ createInterface: rlFactory }));
+    vi.doMock('node:child_process', () => ({ execFileSync: vi.fn() }));
+    vi.doMock('@huggingface/transformers', () => {
+      throw new Error('Cannot find package');
+    });
+
+    const { embed } = await import('../../src/embedder.js');
+
+    await expect(embed(['test'], 'minilm')).rejects.toThrow('process.exit(1)');
+    expect(errorSpy).toHaveBeenCalledWith(
+      expect.stringContaining('Semantic search requires @huggingface/transformers'),
+    );
+    // readline should NOT have been called — no prompt in non-TTY
+    expect(rlFactory).not.toHaveBeenCalled();
+  });
+
+  test('TTY + user declines: prints error and exits', async () => {
+    process.stdin.isTTY = true;
+
+    vi.doMock('node:readline', () => ({
+      createInterface: () => ({
+        question: (_prompt, cb) => cb('n'),
+        close: vi.fn(),
+      }),
+    }));
+    vi.doMock('node:child_process', () => ({ execFileSync: vi.fn() }));
+    vi.doMock('@huggingface/transformers', () => {
+      throw new Error('Cannot find package');
+    });
+
+    const { embed } = await import('../../src/embedder.js');
+
+    await expect(embed(['test'], 'minilm')).rejects.toThrow('process.exit(1)');
+    expect(errorSpy).toHaveBeenCalledWith(
+      expect.stringContaining('Semantic search requires @huggingface/transformers'),
+    );
+  });
+
+  test('TTY + user accepts but npm install fails: prints error and exits', async () => {
+    process.stdin.isTTY = true;
+
+    const execMock = vi.fn(() => {
+      throw new Error('npm ERR!');
+    });
+    vi.doMock('node:readline', () => ({
+      createInterface: () => ({
+        question: (_prompt, cb) => cb('y'),
+        close: vi.fn(),
+      }),
+    }));
+    vi.doMock('node:child_process', () => ({ execFileSync: execMock }));
+    vi.doMock('@huggingface/transformers', () => {
+      throw new Error('Cannot find package');
+    });
+
+    const { embed } = await import('../../src/embedder.js');
+
+    await expect(embed(['test'], 'minilm')).rejects.toThrow('process.exit(1)');
+    expect(execMock).toHaveBeenCalledWith(
+      'npm',
+      ['install', '@huggingface/transformers'],
+      expect.objectContaining({ stdio: 'inherit', timeout: 300_000 }),
+    );
+    expect(errorSpy).toHaveBeenCalledWith(
+      expect.stringContaining('Semantic search requires @huggingface/transformers'),
+    );
+  });
+
+  test('TTY + install succeeds: retries import and loads module', async () => {
+    process.stdin.isTTY = true;
+
+    let importCount = 0;
+    vi.doMock('node:readline', () => ({
+      createInterface: () => ({
+        question: (_prompt, cb) => cb('y'),
+        close: vi.fn(),
+      }),
+    }));
+    vi.doMock('node:child_process', () => ({ execFileSync: vi.fn() }));
+    vi.doMock('@huggingface/transformers', () => {
+      importCount++;
+      if (importCount <= 1) throw new Error('Cannot find package');
+      return {
+        pipeline: async () => async (batch) => ({
+          data: new Float32Array(384 * batch.length),
+        }),
+        cos_sim: () => 0,
+      };
+    });
+
+    const { embed } = await import('../../src/embedder.js');
+
+    const result = await embed(['test text'], 'minilm');
+    expect(result.vectors).toHaveLength(1);
+    expect(result.dim).toBe(384);
+    expect(exitSpy).not.toHaveBeenCalled();
+  });
+});