Index: lucene/src/test/org/apache/lucene/util/automaton/TestMinimize.java
===================================================================
--- lucene/src/test/org/apache/lucene/util/automaton/TestMinimize.java	(revision 0)
+++ lucene/src/test/org/apache/lucene/util/automaton/TestMinimize.java	(revision 0)
@@ -0,0 +1,33 @@
+package org.apache.lucene.util.automaton;
+
+import org.apache.lucene.util.LuceneTestCase;
+
+public class TestMinimize extends LuceneTestCase {
+  public void test() {
+    int num = 10000 * RANDOM_MULTIPLIER;
+    for (int i = 0; i < num; i++) {
+      Automaton a = randomishAutomaton();
+      Automaton b = a.clone();
+      MinimizationOperations.minimize(b);
+      assertTrue(BasicOperations.sameLanguage(a, b));
+    }
+  }
+  
+  private Automaton randomishAutomaton() {
+    // get two random Automata from regexps
+    Automaton a1 = AutomatonTestUtil.randomRegexp(random).toAutomaton();
+    if (random.nextBoolean())
+      a1 = BasicOperations.complement(a1);
+    
+    Automaton a2 = AutomatonTestUtil.randomRegexp(random).toAutomaton();
+    if (random.nextBoolean()) 
+      a2 = BasicOperations.complement(a2);
+    
+    // combine them in random ways
+    switch(random.nextInt(3)) {
+      case 0: return BasicOperations.concatenate(a1, a2);
+      case 1: return BasicOperations.union(a1, a2);
+      default: return BasicOperations.minus(a1, a2);
+    }
+  }
+}

Property changes on: lucene\src\test\org\apache\lucene\util\automaton\TestMinimize.java
___________________________________________________________________
Added: svn:eol-style
   + native

Index: lucene/src/java/org/apache/lucene/util/automaton/BasicOperations.java
===================================================================
--- lucene/src/java/org/apache/lucene/util/automaton/BasicOperations.java	(revision 1026095)
+++ lucene/src/java/org/apache/lucene/util/automaton/BasicOperations.java	(working copy)
@@ -77,6 +77,7 @@
       s.addEpsilon(a2.initial);
     }
     a1.deterministic = deterministic;
+    a1.restoreInvariant(); // nocommit
     //a1.clearHashCode();
     a1.clearNumberedStates();
     a1.checkMinimizeAlways();