diff --git a/spring-boot-project/spring-boot-tools/spring-boot-test-support/src/main/java/org/springframework/boot/testsupport/assertj/SimpleAsyncTaskExecutorAssert.java b/spring-boot-project/spring-boot-tools/spring-boot-test-support/src/main/java/org/springframework/boot/testsupport/assertj/SimpleAsyncTaskExecutorAssert.java
new file mode 100644
index 0000000000..3e7fbde2ab
--- /dev/null
+++ b/spring-boot-project/spring-boot-tools/spring-boot-test-support/src/main/java/org/springframework/boot/testsupport/assertj/SimpleAsyncTaskExecutorAssert.java
@@ -0,0 +1,85 @@
+/*
+ * Copyright 2012-2023 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.boot.testsupport.assertj;
+
+import java.lang.reflect.Field;
+
+import org.assertj.core.api.AbstractAssert;
+import org.assertj.core.api.Assert;
+
+import org.springframework.core.task.SimpleAsyncTaskExecutor;
+import org.springframework.util.ReflectionUtils;
+
+/**
+ * AssertJ {@link Assert} for {@link SimpleAsyncTaskExecutor}.
+ *
+ * @author Moritz Halbritter
+ * @since 3.2.0
+ */
+public final class SimpleAsyncTaskExecutorAssert
+		extends AbstractAssert<SimpleAsyncTaskExecutorAssert, SimpleAsyncTaskExecutor> {
+
+	private SimpleAsyncTaskExecutorAssert(SimpleAsyncTaskExecutor actual) {
+		super(actual, SimpleAsyncTaskExecutorAssert.class);
+	}
+
+	/**
+	 * Verifies that the actual executor uses platform threads.
+	 * @return {@code this} assertion object
+	 * @throws AssertionError if the actual executor doesn't use platform threads
+	 */
+	public SimpleAsyncTaskExecutorAssert usesPlatformThreads() {
+		isNotNull();
+		if (producesVirtualThreads()) {
+			failWithMessage("Expected executor to use platform threads, but it uses virtual threads");
+		}
+		return this;
+	}
+
+	/**
+	 * Verifies that the actual executor uses virtual threads.
+	 * @return {@code this} assertion object
+	 * @throws AssertionError if the actual executor doesn't use virtual threads
+	 */
+	public SimpleAsyncTaskExecutorAssert usesVirtualThreads() {
+		isNotNull();
+		if (!producesVirtualThreads()) {
+			failWithMessage("Expected executor to use virtual threads, but it uses platform threads");
+		}
+		return this;
+	}
+
+	private boolean producesVirtualThreads() {
+		Field field = ReflectionUtils.findField(SimpleAsyncTaskExecutor.class, "virtualThreadDelegate");
+		if (field == null) {
+			throw new IllegalStateException("Field SimpleAsyncTaskExecutor.virtualThreadDelegate not found");
+		}
+		ReflectionUtils.makeAccessible(field);
+		Object virtualThreadDelegate = ReflectionUtils.getField(field, this.actual);
+		return virtualThreadDelegate != null;
+	}
+
+	/**
+	 * Creates a new assertion class with the given {@link SimpleAsyncTaskExecutor}.
+	 * @param actual the {@link SimpleAsyncTaskExecutor}
+	 * @return the assertion class
+	 */
+	public static SimpleAsyncTaskExecutorAssert assertThat(SimpleAsyncTaskExecutor actual) {
+		return new SimpleAsyncTaskExecutorAssert(actual);
+	}
+
+}
diff --git a/spring-boot-project/spring-boot-tools/spring-boot-test-support/src/main/java/org/springframework/boot/testsupport/assertj/package-info.java b/spring-boot-project/spring-boot-tools/spring-boot-test-support/src/main/java/org/springframework/boot/testsupport/assertj/package-info.java
new file mode 100644
index 0000000000..51fb5eaf4e
--- /dev/null
+++ b/spring-boot-project/spring-boot-tools/spring-boot-test-support/src/main/java/org/springframework/boot/testsupport/assertj/package-info.java
@@ -0,0 +1,20 @@
+/*
+ * Copyright 2012-2021 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.
+ */
+
+/**
+ * Custom AssertJ assertions.
+ */
+package org.springframework.boot.testsupport.assertj;
diff --git a/spring-boot-project/spring-boot-tools/spring-boot-test-support/src/test/java/org/springframework/boot/testsupport/assertj/SimpleAsyncTaskExecutorAssertTests.java b/spring-boot-project/spring-boot-tools/spring-boot-test-support/src/test/java/org/springframework/boot/testsupport/assertj/SimpleAsyncTaskExecutorAssertTests.java
new file mode 100644
index 0000000000..a3775298f8
--- /dev/null
+++ b/spring-boot-project/spring-boot-tools/spring-boot-test-support/src/test/java/org/springframework/boot/testsupport/assertj/SimpleAsyncTaskExecutorAssertTests.java
@@ -0,0 +1,47 @@
+/*
+ * Copyright 2012-2023 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.boot.testsupport.assertj;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.EnabledForJreRange;
+import org.junit.jupiter.api.condition.JRE;
+
+import org.springframework.core.task.SimpleAsyncTaskExecutor;
+
+/**
+ * Tests for {@link SimpleAsyncTaskExecutorAssert}.
+ *
+ * @author Moritz Halbritter
+ */
+class SimpleAsyncTaskExecutorAssertTests {
+
+	@Test
+	void usesPlatformThreads() {
+		SimpleAsyncTaskExecutor executor = new SimpleAsyncTaskExecutor();
+		executor.setVirtualThreads(false);
+		SimpleAsyncTaskExecutorAssert.assertThat(executor).usesPlatformThreads();
+	}
+
+	@Test
+	@EnabledForJreRange(min = JRE.JAVA_21)
+	void usesVirtualThreads() {
+		SimpleAsyncTaskExecutor executor = new SimpleAsyncTaskExecutor();
+		executor.setVirtualThreads(true);
+		SimpleAsyncTaskExecutorAssert.assertThat(executor).usesVirtualThreads();
+	}
+
+}