Return DecoratedCall from clone() to preserve its contract. (ReactiveX#363)

DecoratedCall should return an object of the same type (DecoratedCall)
to not break clone() contract on which other objects may relay on.
X.clone() cannot return Y, should return X.

Author: Przemysław Wojnowski

resilience4j-retrofit/src/main/java/io/github/resilience4j/retrofit/internal/DecoratedCall.java

@@ -66,7 +66,7 @@ public boolean isCanceled() {
 
     @Override
     public Call<T> clone() {
-        return call.clone();
+        return new DecoratedCall<>(call.clone());
     }
 
     @Override

resilience4j-retrofit/src/test/java/io/github/resilience4j/retrofit/internal/DecoratedCallTest.java

@@ -8,17 +8,18 @@
 
 import java.io.IOException;
 
+import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.mock;
 
 @RunWith(JUnit4.class)
 public class DecoratedCallTest {
 
+    private final Call<String> call = mock(StringCall.class);
+    private final Call<String> decorated = new DecoratedCall<>(call);
+
     @Test
     public void passThroughCallsToDecoratedObject() throws IOException {
-        final Call<String> call = mock(StringCall.class);
-        final Call<String> decorated = new DecoratedCall<>(call);
-
         decorated.cancel();
         Mockito.verify(call).cancel();
 
@@ -41,6 +42,23 @@ public void passThroughCallsToDecoratedObject() throws IOException {
         Mockito.verify(call).execute();
     }
 
+    @Test
+    public void cloneShouldReturnDecoratedCall() {
+        Call<String> clonedTarget = mock(StringCall.class);
+        Mockito.when(call.clone()).thenReturn(clonedTarget);
+
+        Call<String> clonedDecorator = decorated.clone();
+        Mockito.verify(call).clone();
+        assertThat(clonedDecorator).isInstanceOf(DecoratedCall.class);
+
+        decorated.request();
+        Mockito.verify(call).request();
+        Mockito.verifyNoMoreInteractions(call);
+
+        clonedDecorator.request();
+        Mockito.verify(clonedTarget).request();
+    }
+
     private interface StringCall extends Call<String> {
     }
 }