test(lib): add unit tests for PackageManagerFactory.prototype.find

test/lib/package-managers/package-manager.factory.spec.ts

@@ -0,0 +1,64 @@
+import * as fs from 'fs';
+import {
+  NpmPackageManager,
+  PackageManagerFactory,
+  PnpmPackageManager,
+  YarnPackageManager,
+} from '../../../lib/package-managers';
+
+jest.mock('fs', () => ({
+  promises: {
+    readdir: jest.fn(),
+  },
+}));
+
+describe('PackageManagerFactory', () => {
+  afterAll(() => {
+    jest.clearAllMocks();
+  });
+
+  describe('.prototype.find()', () => {
+    it('should return NpmPackageManager when no lock file is found', async () => {
+      (fs.promises.readdir as jest.Mock).mockResolvedValue([]);
+
+      const whenPackageManager = PackageManagerFactory.find();
+      await expect(whenPackageManager).resolves.toBeInstanceOf(
+        NpmPackageManager,
+      );
+    });
+
+    it('should return YarnPackageManager when "yarn.lock" file is found', async () => {
+      (fs.promises.readdir as jest.Mock).mockResolvedValue(['yarn.lock']);
+
+      const whenPackageManager = PackageManagerFactory.find();
+      await expect(whenPackageManager).resolves.toBeInstanceOf(
+        YarnPackageManager,
+      );
+    });
+
+    it('should return PnpmPackageManager when "pnpm-lock.yaml" file is found', async () => {
+      (fs.promises.readdir as jest.Mock).mockResolvedValue(['pnpm-lock.yaml']);
+
+      const whenPackageManager = PackageManagerFactory.find();
+      await expect(whenPackageManager).resolves.toBeInstanceOf(
+        PnpmPackageManager,
+      );
+    });
+
+    describe('when there are all supported lock files', () => {
+      it('should prioritize "yarn.lock" file over all the others lock files', async () => {
+        (fs.promises.readdir as jest.Mock).mockResolvedValue([
+          'pnpm-lock.yaml',
+          'package-lock.json',
+          // This is intentionally the last element in this array
+          'yarn.lock',
+        ]);
+
+        const whenPackageManager = PackageManagerFactory.find();
+        await expect(whenPackageManager).resolves.toBeInstanceOf(
+          YarnPackageManager,
+        );
+      });
+    });
+  });
+});