Better to use an IllegalStateException rather than assertion in setResult.

Assertions are only for cases where you believe the failure of the condition is impossible.
For cases where external code might mistakenly make an incorrect call, throw an exception.

core/src/main/java/hudson/model/Run.java

@@ -440,9 +440,18 @@ public abstract class Run <JobT extends Job<JobT,RunT>,RunT extends Run<JobT,Run
         return result;
     }
 
+    /**
+     * Sets the {@link #getResult} of this build.
+     * Has no effect when the result is already set and worse than the proposed result.
+     * May only be called after the build has started and before it has moved into post-production
+     * (normally meaning both {@link #isInProgress} and {@link #isBuilding} are true).
+     * @param r the proposed new result
+     * @throws IllegalStateException if the build has not yet started, is in post-production, or is complete
+     */
     public void setResult(@Nonnull Result r) {
-        // state can change only when we are building
-        assert state==State.BUILDING : state;
+        if (state != State.BUILDING) {
+            throw new IllegalStateException("cannot change build result while in " + state);
+        }
 
         // result can only get worse
         if (result==null || r.isWorseThan(result)) {