diff --git a/spring-messaging/src/test/java/org/springframework/messaging/simp/annotation/support/PrincipalMethodArgumentResolverTests.java b/spring-messaging/src/test/java/org/springframework/messaging/simp/annotation/support/PrincipalMethodArgumentResolverTests.java
new file mode 100644
index 00000000000..7ccbb7e79a8
--- /dev/null
+++ b/spring-messaging/src/test/java/org/springframework/messaging/simp/annotation/support/PrincipalMethodArgumentResolverTests.java
@@ -0,0 +1,73 @@
+/*
+ * Copyright 2002-2019 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.messaging.simp.annotation.support;
+
+import java.security.Principal;
+import java.util.Collections;
+import java.util.Optional;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.core.MethodParameter;
+import org.springframework.messaging.Message;
+import org.springframework.messaging.handler.invocation.ResolvableMethod;
+import org.springframework.messaging.simp.SimpMessageHeaderAccessor;
+import org.springframework.messaging.support.GenericMessage;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Unit tests for {@link PrincipalMethodArgumentResolver}.
+ *
+ * @author Rossen Stoyanchev
+ * @author Johnny Lim
+ */
+public class PrincipalMethodArgumentResolverTests {
+
+	private final PrincipalMethodArgumentResolver resolver = new PrincipalMethodArgumentResolver();
+
+	private final ResolvableMethod testMethod = ResolvableMethod.on(getClass()).named("handle").build();
+
+
+	@Test
+	public void supportsParameter() {
+		assertThat(this.resolver.supportsParameter(this.testMethod.arg(Principal.class))).isTrue();
+		assertThat(this.resolver.supportsParameter(this.testMethod.arg(Optional.class, Principal.class))).isTrue();
+	}
+
+
+	@Test
+	public void resolverArgument() {
+		Principal user = () -> "Joe";
+		Message<String> message = new GenericMessage<>("Hello, world!",
+				Collections.singletonMap(SimpMessageHeaderAccessor.USER_HEADER, user));
+
+		MethodParameter param = this.testMethod.arg(Principal.class);
+		Object actual = this.resolver.resolveArgument(param, message);
+		assertThat(actual).isSameAs(user);
+
+		param = this.testMethod.arg(Optional.class, Principal.class);
+		actual = this.resolver.resolveArgument(param, message);
+		assertThat(actual).isInstanceOf(Optional.class).extracting(o -> ((Optional<?>) o).get()).isSameAs(user);
+	}
+
+
+	@SuppressWarnings("unused")
+	void handle(Principal user, Optional<Principal> optionalUser) {
+	}
+
+}
diff --git a/spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/PrincipalMethodArgumentResolverTests.java b/spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/PrincipalMethodArgumentResolverTests.java
index 4ad26e732e3..32078174ff8 100644
--- a/spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/PrincipalMethodArgumentResolverTests.java
+++ b/spring-webflux/src/test/java/org/springframework/web/reactive/result/method/annotation/PrincipalMethodArgumentResolverTests.java
@@ -42,7 +42,7 @@ public class PrincipalMethodArgumentResolverTests {
 	private final PrincipalMethodArgumentResolver resolver =
 			new PrincipalMethodArgumentResolver(ReactiveAdapterRegistry.getSharedInstance());
 
-	private ResolvableMethod testMethod = ResolvableMethod.on(getClass()).named("handle").build();
+	private final ResolvableMethod testMethod = ResolvableMethod.on(getClass()).named("handle").build();
 
 
 	@Test
@@ -55,24 +55,22 @@ public class PrincipalMethodArgumentResolverTests {
 
 	@Test
 	public void resolverArgument() {
-		BindingContext context = new BindingContext();
 		Principal user = () -> "Joe";
 		ServerWebExchange exchange = MockServerWebExchange.from(MockServerHttpRequest.get("/"))
 				.mutate().principal(Mono.just(user)).build();
 
+		BindingContext context = new BindingContext();
 		MethodParameter param = this.testMethod.arg(Principal.class);
 		Object actual = this.resolver.resolveArgument(param, context, exchange).block();
 		assertThat(actual).isSameAs(user);
 
 		param = this.testMethod.arg(Mono.class, Principal.class);
 		actual = this.resolver.resolveArgument(param, context, exchange).block();
-		assertThat(Mono.class.isAssignableFrom(actual.getClass())).isTrue();
-		assertThat(((Mono<?>) actual).block()).isSameAs(user);
+		assertThat(actual).isInstanceOf(Mono.class).extracting(o -> ((Mono<?>) o).block()).isSameAs(user);
 
 		param = this.testMethod.arg(Single.class, Principal.class);
 		actual = this.resolver.resolveArgument(param, context, exchange).block();
-		assertThat(Single.class.isAssignableFrom(actual.getClass())).isTrue();
-		assertThat(((Single<?>) actual).blockingGet()).isSameAs(user);
+		assertThat(actual).isInstanceOf(Single.class).extracting(o -> ((Single<?>) o).blockingGet()).isSameAs(user);
 	}