refactor for cross platform use

__tests__/util.test.ts

@@ -0,0 +1,19 @@
+import { isTag, paths } from '../src/util';
+import * as assert from 'assert';
+
+describe('util', () => {
+  describe('isTag', () => {
+    it('returns true for tags', async () => {
+      assert.equal(isTag('refs/tags/foo'), true)
+    });
+    it ('returns false for other kinds of refs', async () => {
+      assert.equal(isTag('refs/heads/master'), false)
+    })
+  })
+
+  describe('paths', () => {
+    it('resolves files given a set of paths', async () => {
+      assert.deepStrictEqual(paths(["tests/data/**/*"]), ['tests/data/foo/bar.txt'])
+    });
+  })
+});