Fix test

spring-cloud-stream/src/test/java/org/springframework/cloud/stream/function/SourceToFunctionsSupportTests.java

@@ -23,6 +23,7 @@ import java.util.function.Supplier;
 
 import org.junit.Rule;
 import org.junit.Test;
+import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.rules.ExpectedException;
 import reactor.core.publisher.Flux;
@@ -61,6 +62,10 @@ public class SourceToFunctionsSupportTests {
 	public void before() {
 		System.clearProperty("spring.cloud.stream.function.definition");
 	}
+	@AfterEach
+	public void after() {
+		System.clearProperty("spring.cloud.stream.function.definition");
+	}
 
 	@Test
 	public void testFunctionIsAppliedToExistingMessageSource() {