Improve fail message when server is still running

Makes it easier to find out why the test fails. The developer now sees
a message like

    SFTP server is still running on port 12345.

instead of

    Expecting code to raise a throwable.

Author: stefanbirkner

pom.xml

@@ -9,7 +9,7 @@
     </parent>
 
     <artifactId>fake-sftp-server-rule</artifactId>
-    <version>2.0.0-SNAPSHOT</version>
+    <version>1.1.1-SNAPSHOT</version>
     <packaging>jar</packaging>
 
     <name>Fake SFTP Server Rule</name>

src/test/java/com/github/stefanbirkner/fakesftpserver/rule/FakeSftpServerRuleTest.java

@@ -23,6 +23,7 @@
 import static org.apache.commons.io.IOUtils.toByteArray;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
+import static org.assertj.core.api.Assertions.catchThrowable;
 
 /* Wording according to the draft:
  * http://tools.ietf.org/html/draft-ietf-secsh-filexfer-13
@@ -591,7 +592,14 @@ public void after_an_erroneous_test_SFTP_server_is_shutdown() {
         private void assertConnectionToSftpServerNotPossible(
             FakeSftpServerRule sftpServer
         ) {
-            assertThatThrownBy(() -> connectToServer(sftpServer))
+            Throwable throwable = catchThrowable(
+                () -> connectToServer(sftpServer)
+            );
+            assertThat(throwable)
+                .withFailMessage(
+                    "SFTP server is still running on port %d.",
+                    sftpServer.getPort()
+                )
                 .hasCauseInstanceOf(ConnectException.class);
         }
     }