Up timeout for optional test to pass

src/test/java/uk/ac/rhul/cs/javatester/UnitTests.java

@@ -36,7 +36,7 @@ public class UnitTests {
         = "uk.ac.rhul.cs.javatester.solution.NullPtrMethod";
 
     @Rule
-    public Timeout globalTimeout = Timeout.seconds(10);
+    public Timeout globalTimeout = Timeout.seconds(20);
 
     @Test
     public void testMainClassFail() throws IOException {