Don't forget to pop the condition off the stack

src/org/jetbrains/eval4j/interpreterLoop.kt

@@ -114,12 +114,14 @@ fun interpreterLoop(
                     RETURN -> return ValueReturned(VOID_VALUE)
                     IFEQ, IFNE, IFLT, IFGE, IFGT, IFLE, IFNULL, IFNONNULL -> {
                         if (interpreter.checkUnaryCondition(frame.getStack(0)!!, insnOpcode)) {
+                            frame.execute(currentInsn, interpreter)
                             goto((currentInsn as JumpInsnNode).label)
                             continue
                         }
                     }
                     IF_ICMPEQ, IF_ICMPNE, IF_ICMPLT, IF_ICMPGE, IF_ICMPGT, IF_ICMPLE, IF_ACMPEQ, IF_ACMPNE -> {
                         if (interpreter.checkBinaryCondition(frame.getStack(0)!!, frame.getStack(1)!!, insnOpcode)) {
+                            frame.execute(currentInsn, interpreter)
                             goto((currentInsn as JumpInsnNode).label)
                             continue
                         }

test/org/jetbrains/eval4j/test/TestData.java

@@ -35,4 +35,31 @@ class TestData {
     static double returnDouble() {
         return 2.0d;
     }
+
+    static int variable() {
+        int i = 153;
+        return i;
+    }
+
+    static int unaryMinus() {
+        int i = 153;
+        return -i;
+    }
+
+    static int ifThen() {
+        boolean a = true;
+        if (a)
+            return 2;
+        return 1;
+    }
+
+    static int ifElse() {
+        boolean a = false;
+        if (a) {
+            return 2;
+        }
+        else {
+            return 1;
+        }
+    }
 }