vm: add some tests for PACK instruction

pkg/vm/stack.go

@@ -84,6 +84,18 @@ func (e *Element) Bytes() []byte {
 	return e.value.Value().([]byte)
 }
 
+// Array attempts to get the underlying value of the element as an array of
+// other items. Will panic if the item type is different which will be caught
+// by the VM.
+func (e *Element) Array() []StackItem {
+	switch t := e.value.(type) {
+	case *ArrayItem:
+		return t.value
+	default:
+		panic("element is not an array")
+	}
+}
+
 // Stack represents a Stack backed by a double linked list.
 type Stack struct {
 	top  Element

pkg/vm/vm_test.go

@@ -633,6 +633,46 @@ func TestRIGHTBadLen(t *testing.T) {
 	assert.Equal(t, true, vm.state.HasFlag(faultState))
 }
 
+func TestPACKBadLen(t *testing.T) {
+	prog := makeProgram(PACK)
+	vm := load(prog)
+	vm.estack.PushVal(1)
+	vm.Run()
+	assert.Equal(t, true, vm.state.HasFlag(faultState))
+}
+
+func TestPACKGoodZeroLen(t *testing.T) {
+	prog := makeProgram(PACK)
+	vm := load(prog)
+	vm.estack.PushVal(0)
+	vm.Run()
+	assert.Equal(t, false, vm.state.HasFlag(faultState))
+	assert.Equal(t, 1, vm.estack.Len())
+	assert.Equal(t, []StackItem{}, vm.estack.Peek(0).Array())
+}
+
+func TestPACKGood(t *testing.T) {
+	prog := makeProgram(PACK)
+	elements := []int{55, 34, 42}
+	vm := load(prog)
+	// canary
+	vm.estack.PushVal(1)
+	for i := len(elements) - 1; i >= 0; i-- {
+		vm.estack.PushVal(elements[i])
+	}
+	vm.estack.PushVal(len(elements))
+	vm.Run()
+	assert.Equal(t, false, vm.state.HasFlag(faultState))
+	assert.Equal(t, 2, vm.estack.Len())
+	a := vm.estack.Peek(0).Array()
+	assert.Equal(t, len(elements), len(a))
+	for i := 0; i < len(elements); i++ {
+		e := a[i].Value().(*big.Int)
+		assert.Equal(t, int64(elements[i]), e.Int64())
+	}
+	assert.Equal(t, int64(1), vm.estack.Peek(1).BigInt().Int64())
+}
+
 func makeProgram(opcodes ...Instruction) []byte {
 	prog := make([]byte, len(opcodes)+1) // RET
 	for i := 0; i < len(opcodes); i++ {