pkg/vm/stack: improve Array testing code slightly

GolangCI complained:
  testArray is unused (from deadcode)

But this function was actually wrong being a copy-paste of testMakeStackMap(),
it also didn't conform to testMake... naming scheme, so this fixes it. To make
thing more uniform NewArray() was also changed to return error, map_test.go
code adjusted to this changes and finally array_test.go was added as a stub
for future Array testing.

pkg/vm/stack/array.go

@@ -22,11 +22,11 @@ func (a *Array) Value() []Item {
 }
 
 // NewArray returns a new Array.
-func NewArray(val []Item) *Array {
+func NewArray(val []Item) (*Array, error) {
 	return &Array{
 		&abstractItem{},
 		val,
-	}
+	}, nil
 }
 
 // Hash overrides the default abstract hash method.

pkg/vm/stack/array_test.go

@@ -0,0 +1,16 @@
+package stack
+
+import (
+	"testing"
+
+// it's a stub at the moment, but will need it anyway
+//	"github.com/stretchr/testify/assert"
+)
+
+func TestArray(t *testing.T) {
+	var a Item = testMakeStackInt(t, 3)
+	var b Item = testMakeStackInt(t, 6)
+	var c Item = testMakeStackInt(t, 9)
+	var ta = testMakeArray(t, []Item{a, b, c})
+	_ = ta
+}

pkg/vm/stack/map_test.go

@@ -16,7 +16,7 @@ func TestMap(t *testing.T) {
 		b: a,
 	})
 	var e = NewContext([]byte{1, 2, 3, 4})
-	var f = NewArray([]Item{a, b})
+	var f = testMakeArray(t, []Item{a, b})
 
 	val := map[Item]Item{
 		a: c,
@@ -47,7 +47,7 @@ func TestMap(t *testing.T) {
 	valueE, _ := m.ValueOfKey(NewContext([]byte{1, 2, 3, 4}))
 	assert.Equal(t, d, valueE)
 
-	valueF, _ := m.ValueOfKey(NewArray([]Item{a, b}))
+	valueF, _ := m.ValueOfKey(testMakeArray(t, []Item{a, b}))
 	assert.Equal(t, e, valueF)
 
 	valueX, _ := m.ValueOfKey(NewByteArray([]byte{1, 2, 35}))
@@ -100,7 +100,7 @@ func TestMap(t *testing.T) {
 	assert.Nil(t, err)
 	assert.Equal(t, true, checkContext.Value())
 
-	checkArray, err := CompareHash(f, NewArray([]Item{a, b}))
+	checkArray, err := CompareHash(f, testMakeArray(t, []Item{a, b}))
 	assert.Nil(t, err)
 	assert.Equal(t, true, checkArray.Value())
 }

pkg/vm/stack/test_helper.go

@@ -49,8 +49,8 @@ func testMakeStackMap(t *testing.T, m map[Item]Item) *Map {
 	return a
 }
 
-func testArray(t *testing.T, m map[Item]Item) *Map {
+func testMakeArray(t *testing.T, v []Item) *Array {
-	a, err := NewMap(m)
+	a, err := NewArray(v)
 	assert.Nil(t, err)
 	return a
 }