Add tests

__tests__/installer.test.ts

@@ -0,0 +1,14 @@
+import fs = require('fs');
+import * as installer from '../src/installer';
+
+describe('installer', () => {
+  it('acquires v0.117.0 version of GoReleaser', async () => {
+    const goreleaser = await installer.getGoReleaser('v0.117.0');
+    expect(fs.existsSync(goreleaser)).toBe(true);
+  }, 100000);
+
+  it('acquires latest version of GoReleaser', async () => {
+    const goreleaser = await installer.getGoReleaser('latest');
+    expect(fs.existsSync(goreleaser)).toBe(true);
+  }, 100000);
+});