=tck flop eagerly

Author: ktoso

tck/src/main/java/org/reactivestreams/tck/TestEnvironment.java

@@ -907,6 +907,8 @@ public void complete(T value) {
       if (_value.compareAndSet(null, value)) {
         // we add the value to the queue such to wake up any expectCompletion which was triggered before complete() was called
         abq.add(value);
+      } else {
+        env.flop(String.format("Cannot complete a promise more than once! Present value: %s", value));
       }
     }