Validate URLs

test/manifique_test.rb

@@ -5,6 +5,14 @@ class ManifiqueTest < Minitest::Test
     refute_nil ::Manifique::VERSION
   end
 
+  def test_init_without_url
+    assert_raises(RuntimeError) { Manifique::Agent.new }
+  end
+
+  def test_init_with_invalid_url
+    assert_raises(RuntimeError) { Manifique::Agent.new(url: "htp:/foo.com") }
+  end
+
   def test_fetch_metadata
     agent = Manifique::Agent.new(url: 'https://example.com')
     assert_equal agent.fetch_metadata, 'https://example.com'