Allow port to be changed using MTT_PORT environment variable.

tests/step_defs/test_server_start.py

@@ -1,24 +1,40 @@
 """Interpratures for server start features."""
 
-from pytest_bdd import given, scenarios, then, when
+from pytest_bdd import given, parsers, scenarios, then, when
 
 scenarios("../features/server_start.feature")
 
+
 @given("a server")
-def create_server(server):
+def create_server():
     """Set up a server."""
 
+
+@given(parsers.re(r"address is set to (?P<addr>\S+)"))
+def set_server_address(server, addr):
+    """Set the Server address."""
+    server.address = addr
+
+
+@given("port is changed to something different")
+def set_to_safe_port(server):
+    """Set the app server to an unused port."""
+    server.set_safe_port()
+
+
 @given("it is running")
 def start_server(server):
     """Start up the server."""
     server.start()
 
+
 @when("the home page is accessed")
 def access_home_page(server, page):
     """Access the home page."""
     url = f"http://{server.address}:{server.port}/"
     page.request_url(url)
 
+
 @then("the status should be OK")
 def check_for_ok(page):
     """Is the page status code 200"""