Extract assertConnectionToSftpServerNotPossible.

Improve readability of the code. The reader can now read the test
without knowing how the test checks that it cannot connect to the
server. In addition they don't have to understand that the extracted
code means that a connection to the server is checked.

Author: stefanbirkner

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

@@ -572,10 +572,7 @@ public void after_a_successful_test_SFTP_server_is_shutdown() {
                 () -> {},
                 sftpServer
             );
-            Throwable exception = exceptionThrownBy(
-                () -> connectToServer(sftpServer)
-            );
-            assertThat(exception).hasCauseInstanceOf(ConnectException.class);
+            assertConnectionToSftpServerNotPossible(sftpServer);
         }
 
         @Test
@@ -587,10 +584,14 @@ public void after_an_erroneous_test_SFTP_server_is_shutdown() {
                 },
                 sftpServer
             );
-            Throwable exception = exceptionThrownBy(
-                () -> connectToServer(sftpServer)
-            );
-            assertThat(exception).hasCauseInstanceOf(ConnectException.class);
+            assertConnectionToSftpServerNotPossible(sftpServer);
+        }
+
+        private void assertConnectionToSftpServerNotPossible(
+            FakeSftpServerRule sftpServer
+        ) {
+            assertThatThrownBy(() -> connectToServer(sftpServer))
+                .hasCauseInstanceOf(ConnectException.class);
         }
     }