Modify notCreateLongLivedThreadsAfterExecution to count live threads.

spring-cloud-dataflow-common/spring-cloud-dataflow-common-test-docker/src/test/java/org/springframework/cloud/dataflow/common/test/docker/compose/execution/CommandTests.java

@@ -18,7 +18,9 @@
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Set;
 import java.util.function.Consumer;
+import java.util.stream.Collectors;
 
 import org.apache.commons.io.IOUtils;
 import org.junit.jupiter.api.BeforeEach;
@@ -90,10 +92,12 @@ void giveTheOutputToTheSpecifiedConsumerAsItIsAvailable() throws Exception {
 
     @Test
     void notCreateLongLivedThreadsAfterExecution() throws Exception {
-        int preThreadCount = Thread.getAllStackTraces().entrySet().size();
+		Set<Thread> preEntries = Thread.getAllStackTraces().keySet().stream().filter(Thread::isAlive).collect(Collectors.toSet());
+		int preThreadCount = preEntries.size();
         dockerComposeCommand.execute(errorHandler, true, "rm", "-f");
-        int postThreadCount = Thread.getAllStackTraces().entrySet().size();
-		assertThat(preThreadCount == postThreadCount).as("command thread pool has exited").isTrue();
+		Set<Thread> postEntries = Thread.getAllStackTraces().keySet().stream().filter(Thread::isAlive).collect(Collectors.toSet());
+		int postThreadCount = postEntries.size();
+		assertThat(postThreadCount).as(()-> "command thread pool has exited with extra threads:" + postEntries.removeAll(preEntries)).isEqualTo(preThreadCount);
     }
 
     private void givenTheUnderlyingProcessHasOutput(String output) {