add a bunch of tests.

nip04.test.js

@@ -0,0 +1,14 @@
+/* eslint-env jest */
+
+const {nip04, getPublicKey, generatePrivateKey} = require('./cjs')
+
+test('encrypt and decrypt message', () => {
+  let sk1 = generatePrivateKey()
+  let sk2 = generatePrivateKey()
+  let pk1 = getPublicKey(sk1)
+  let pk2 = getPublicKey(sk2)
+
+  expect(nip04.decrypt(sk2, pk1, nip04.encrypt(sk1, pk2, 'hello'))).toEqual(
+    'hello'
+  )
+})