use testify tool
 go get -v github.com/stretchr/testify/assert
package car
import (
	"github.com/stretchr/testify/assert"
	"testing"
)
func TestNewWithAssert(t *testing.T) {
	c, err := New("", 100)
	assert.NotNil(t, err)
	assert.Error(t, err)
	assert.Nil(t, c)
}

只單獨測試func
go test -v -run={func name}