add a couple of context tests around keys with colliding hashcodes (#2114)

* add a couple of context tests around keys with colliding hashcodes

* add a test for an empty context

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

@@ -0,0 +1,37 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.context;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+class DefaultContextTest {
+
+  @Test
+  void emptyContext() {
+    assertThat(new DefaultContext().get(new HashCollidingKey())).isEqualTo(null);
+  }
+
+  @Test
+  void hashcodeCollidingKeys() {
+    DefaultContext context = new DefaultContext();
+    HashCollidingKey cheese = new HashCollidingKey();
+    HashCollidingKey wine = new HashCollidingKey();
+
+    Context twoKeys = context.with(cheese, "whiz").with(wine, "boone's farm");
+
+    assertThat(twoKeys.get(wine)).isEqualTo("boone's farm");
+    assertThat(twoKeys.get(cheese)).isEqualTo("whiz");
+  }
+
+  private static class HashCollidingKey implements ContextKey<String> {
+    @Override
+    public int hashCode() {
+      return 1;
+    }
+  }
+}

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

@@ -0,0 +1,34 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.context;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+
+class PersistentHashArrayMappedTrieTest {
+
+  @Test
+  void hashCollisions() {
+    HashCollidingKey cheese = new HashCollidingKey();
+    HashCollidingKey wine = new HashCollidingKey();
+    PersistentHashArrayMappedTrie.Node<HashCollidingKey, String> root =
+        PersistentHashArrayMappedTrie.put(null, cheese, "cheddar");
+
+    PersistentHashArrayMappedTrie.Node<HashCollidingKey, String> child =
+        PersistentHashArrayMappedTrie.put(root, wine, "Pinot Noir");
+
+    assertThat(PersistentHashArrayMappedTrie.get(child, cheese)).isEqualTo("cheddar");
+    assertThat(PersistentHashArrayMappedTrie.get(child, wine)).isEqualTo("Pinot Noir");
+  }
+
+  private static class HashCollidingKey {
+    @Override
+    public int hashCode() {
+      return 1;
+    }
+  }
+}