test: cover MailerUrlForTest, welcome and MessageEncryptorTest

test/test_message_encryptor.rb

@@ -0,0 +1,59 @@
+require 'minitest/autorun'
+require 'prism'
+
+class MessageEncryptorTest < Minitest::Test
+  def setup
+    @key = Prism::MessageEncryptor.derive_key('super-secret-app-key')
+    @encryptor = Prism::MessageEncryptor.new(@key)
+  end
+
+  def test_derived_key_has_correct_length
+    assert_equal 32, @key.bytesize
+  end
+
+  def test_derive_key_is_deterministic_for_same_secret_and_salt
+    assert_equal @key, Prism::MessageEncryptor.derive_key('super-secret-app-key')
+  end
+
+  def test_derive_key_differs_per_salt
+    other = Prism::MessageEncryptor.derive_key('super-secret-app-key', salt: 'other-salt')
+    refute_equal @key, other
+  end
+
+  def test_round_trips_a_hash
+    token = @encryptor.encrypt_and_sign('admin' => true, 'user_id' => 7)
+    assert_equal({ 'admin' => true, 'user_id' => 7 }, @encryptor.decrypt_and_verify(token))
+  end
+
+  def test_ciphertext_does_not_contain_plaintext
+    token = @encryptor.encrypt_and_sign('super-secret-value-xyz')
+    refute_includes token, 'super-secret-value-xyz'
+  end
+
+  def test_two_encryptions_of_same_value_differ
+    first = @encryptor.encrypt_and_sign('same value')
+    second = @encryptor.encrypt_and_sign('same value')
+    refute_equal first, second
+  end
+
+  def test_tampered_ciphertext_fails_to_decrypt
+    token = @encryptor.encrypt_and_sign('user_id' => 1)
+    encrypted, iv, tag = token.split('--', 3)
+    tampered = "#{encrypted}AA--#{iv}--#{tag}"
+    assert_raises(Prism::MessageEncryptor::InvalidMessage) { @encryptor.decrypt_and_verify(tampered) }
+  end
+
+  def test_wrong_key_cannot_decrypt
+    token = @encryptor.encrypt_and_sign('user_id' => 1)
+    other = Prism::MessageEncryptor.new(Prism::MessageEncryptor.derive_key('a-completely-different-key'))
+    assert_raises(Prism::MessageEncryptor::InvalidMessage) { other.decrypt_and_verify(token) }
+  end
+
+  def test_malformed_message_raises
+    assert_raises(Prism::MessageEncryptor::InvalidMessage) { @encryptor.decrypt_and_verify('garbage') }
+  end
+
+  def test_rejects_key_of_wrong_length
+    assert_raises(ArgumentError) { Prism::MessageEncryptor.new('too-short') }
+  end
+end