Add type check to key_base '==' operator

lib/jwt/jwk/key_base.rb

@@ -38,7 +38,7 @@ def []=(key, value)
       end
 
       def ==(other)
-        self[:kid] == other[:kid]
+        other.is_a?(::JWT::JWK::KeyBase) && self[:kid] == other[:kid]
       end
 
       alias eql? ==

spec/jwk/hmac_spec.rb

@@ -82,4 +82,36 @@
       end
     end
   end
+
+  describe '#==' do
+    it 'is equal to itself' do
+      other = jwk
+      expect(jwk == other).to eq true
+    end
+
+    it 'is equal to a clone of itself' do
+      other = jwk.clone
+      expect(jwk == other).to eq true
+    end
+
+    it 'is not equal to nil' do
+      other = nil
+      expect(jwk == other).to eq false
+    end
+
+    it 'is not equal to boolean true' do
+      other = true
+      expect(jwk == other).to eq false
+    end
+
+    it 'is not equal to a non-key' do
+      other = Object.new
+      expect(jwk == other).to eq false
+    end
+
+    it 'is not equal to a different key' do
+      other = described_class.new('other-key')
+      expect(jwk == other).to eq false
+    end
+  end
 end