Add test that shows how context keys are special (#7330)

Author: breedx-splk

context/src/test/java/io/opentelemetry/context/ContextTest.java

@@ -7,6 +7,7 @@
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.awaitility.Awaitility.await;
+import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyLong;
 import static org.mockito.Mockito.doNothing;
@@ -108,6 +109,12 @@ void attachSameTwice() {
     assertThat(Context.current().get(ANIMAL)).isNull();
   }
 
+  @Test
+  void keyEqualityIsInstanceCheck() {
+    Context context = Context.current().with(ContextKey.named("animal"), "cat");
+    assertNull(context.get(ContextKey.named("animal"))); // yup
+  }
+
   @Test
   void newThreadStartsWithRoot() throws Exception {
     Context context = Context.current().with(ANIMAL, "cat");