Restructure source and tests

__tests__/wait.test.js

@@ -0,0 +1,24 @@
+/**
+ * Unit tests for src/wait.ts
+ */
+const { wait } = require('../src/wait')
+const { expect } = require('@jest/globals')
+
+describe('wait.ts', () => {
+  it('throws an invalid number', async () => {
+    const input = parseInt('foo', 10)
+    expect(isNaN(input)).toBe(true)
+
+    await expect(wait(input)).rejects.toThrow('milliseconds not a number')
+  })
+
+  it('waits with a valid number', async () => {
+    const start = new Date()
+    await wait(500)
+    const end = new Date()
+
+    const delta = Math.abs(end.getTime() - start.getTime())
+
+    expect(delta).toBeGreaterThan(450)
+  })
+})