Added test for GroovyBackend to ensure the ThreadLocal is in place

groovy/src/test/java/cucumber/runtime/groovy/ParallelTest.java

@@ -0,0 +1,51 @@
+package cucumber.runtime.groovy;
+
+import cucumber.runtime.io.ResourceLoader;
+import groovy.lang.Closure;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.runners.MockitoJUnitRunner;
+
+
+@RunWith(MockitoJUnitRunner.class)
+public class ParallelTest {
+    @Mock
+    ResourceLoader resourceLoader;
+    @Mock
+    Closure closure;
+
+    @Test(expected = RuntimeException.class)
+    public void exception_throw_when_world_already_set_on_same_thread() {
+        GroovyBackend groovyBackend = new GroovyBackend(resourceLoader);
+        groovyBackend.registerWorld(closure);
+        groovyBackend.registerWorld(closure);
+    }
+
+    @Test
+    public void can_have_a_new_backend_on_a_different_thread() {
+        new GroovyBackend(resourceLoader);
+        Thread interactWithBackendThread = new Thread(new Runnable(){
+            @Override
+            public void run() {
+                try {
+                    GroovyBackend.getInstance().registerWorld(closure);
+                } catch (NullPointerException e){
+                    // This is what we want as there should be no GroovyBackend on this thread
+                }
+            }
+        });
+        runAndWait(interactWithBackendThread);
+        GroovyBackend.getInstance().registerWorld(closure);
+    }
+
+    private void runAndWait(Thread interactWithBackendThread) {
+        interactWithBackendThread.start();
+        try {
+            interactWithBackendThread.join();
+        } catch (InterruptedException e) {
+            throw new RuntimeException("Doh");
+        }
+    }
+
+}