Add test for replace bug

src/test/java/org/luaj/AllTests.java

@@ -10,6 +10,7 @@ public class AllTests {
 		
 		// debug tests
 		TestSuite vm = new TestSuite("VM");
+		vm.addTestSuite(org.luaj.vm.LuaStateTest.class);
 		vm.addTestSuite(org.luaj.vm.LoadStateTest.class);
 		vm.addTestSuite(org.luaj.vm.LStringTest.class);
 		vm.addTestSuite(org.luaj.vm.MathLibTest.class);

src/test/java/org/luaj/vm/LuaStateTest.java

@@ -0,0 +1,25 @@
+package org.luaj.vm;
+
+import java.io.IOException;
+
+import junit.framework.TestCase;
+
+import org.luaj.TestPlatform;
+
+public class LuaStateTest extends TestCase {
+	LuaState vm;
+
+	protected void setUp() throws Exception {
+        Platform.setInstance(new TestPlatform());
+		vm = Platform.newLuaState();		
+	}
+	
+	public void testPushnilReplaceSettop() throws IOException {
+		vm.pushnil();
+		vm.replace(1);
+		vm.settop(1);
+		assertEquals( 1, vm.gettop() );
+		assertEquals( LNil.NIL, vm.topointer(1) );
+		assertEquals( LNil.NIL, vm.topointer(-1) );
+	}
+}