为什么我的C＃TestClass类（错误地）抱怨其父级没有无参数构造函数？

Question

I am doing some TDD in C# (Visual Studio 2012) using MSTest. I have a class declared with the [TestClass] attribute. My test class inherits from the class I am trying to test.

The parent class has a parameterless constructor, and yet I am getting a build error

'RatingsClass.OutputLine' does not contain a constructor that takes 0 arguments

Here is my base class with its parameterless constructor:

namespace RatingsClasses
{
    public class OutputLine
    {
        public OutputLine()
        {
            Initialise("Parameterless constructor called");
        }
(and so on)

Here is the test class which inherits from the base class. This causes the following build error:

'RatingsClass.OutputLine' does not contain a constructor that takes 0 arguments

Code:

using RatingsClasses;

namespace RatingsKataV2
{
    [TestClass]
    public class RatingsTests: OutputLine
    {
        [TestMethod]
        public void TestSingleTripRatingIs20()
        {
(and so on)

Also when I try to call the base class's parameterless constructor directly from the derived class's constructor, I get lots of red squiggly lines and syntax errors such as Constructor must have body and Unexpected token .

Here is my attempt to call the base constructor explicitly:

using RatingsClasses;

namespace RatingsKataV2
{
    [TestClass]
    public class RatingsTests: OutputLine
    {
        public RatingsTests(): OutputLine()
        {

        }
(the rest of the class goes here)

What am I doing wrong?

The reason I am doing it this way is that I would like to test the various private members of my base class are being populated correctly. Rather than provide getters and setters or make those members public, it seemed to make sense that my test class simply inherit from the class it is testing, so that it can directly access those private members. Is there a better way of doing this?

Answer 1

Your syntax is wrong for calling the base constructor. You should use the base keyword:

public RatingsTest()
    : base()
{

}

Answer 2

The TestClass attribute is for classes that contain unit tests, not for classes that are the targets of those tests. By deriving from the target under test, you are also extending that target to RatingsTests.

RatingsTests should not need to inherit from OutputLine in order to test, but the constructor shoud read.

public RatingsTests(): base() {}

Answer 3

You use base to explicitly choose the constructor of the the base class that should be used:

public RatingsTests() : base()
{
}

However, this is unnecessary, because the parameterless constructor is the default one being used when this is omitted.

The first code you showed should work, so I guess that your actual code is different or you have a second class called OutputLine somewhere in your code base.

Make sure that you are using the correct OutputLine class and that this class actually has a public parameterless constructor. If public is missing, it is automatically private and can't be used by a derived class.