Fix minor issues raised by `golint` and `go vet`

engine/context_test.go

@@ -57,7 +57,7 @@ func TestContextExec(t *testing.T) {
 	for _, tt := range execTests {
 		script, err := NewScript(tt.name, tt.script)
 		if err != nil {
-			t.Errorf("Could not create temporary file for testing: %s", tt.name, err)
+			t.Errorf("Could not create temporary file '%s' for testing: %s", tt.name, err)
 			continue
 		}
 

engine/receiver.go

@@ -130,7 +130,7 @@ func (o *ReceiverObject) Call(name string, args []interface{}) *Value {
 		return nil
 	}
 
-	in := make([]reflect.Value, 0)
+	var in []reflect.Value
 	for _, v := range args {
 		in = append(in, reflect.ValueOf(v))
 	}

engine/value_test.go

@@ -541,7 +541,7 @@ func TestValuePtr(t *testing.T) {
 	}
 
 	if val.Ptr() == nil {
-		t.Errorf("Value.Ptr('%v'): Unable to create pointer from value")
+		t.Errorf("Value.Ptr('%v'): Unable to create pointer from value", 42)
 	}
 }