{"id":3579,"date":"2019-11-28T20:00:25","date_gmt":"2019-11-28T18:00:25","guid":{"rendered":"https:\/\/mariusbancila.ro\/blog\/?p=3579"},"modified":"2019-11-28T15:24:41","modified_gmt":"2019-11-28T13:24:41","slug":"data-driven-unit-tests-for-managed-code","status":"publish","type":"post","link":"https:\/\/mariusbancila.ro\/blog\/2019\/11\/28\/data-driven-unit-tests-for-managed-code\/","title":{"rendered":"Data-driven unit tests for managed code"},"content":{"rendered":"

The Microsoft unit testing code for managed code allows to create test methods that are executed with data automatically fetched from an external data source. This is very helpful because we can extend the data sets without modifying the test code. An external data source can be an SQL database, a CSV file or Excel document, an XML document, or anything else for which a provider for .NET exists. In this article, I will show how you can define test data using all these types of source and execute unit testing methods with it.<\/p>\n

\nThis feature is available only for .NET Framework.
\nAt this time, data-driven unit testing from a data source is not supported for .NET Core.\n<\/div>\n

<\/p>\n

\nDemo test project source:
\n
\n\n\tDataDrivenTestsDemo.zip\t(3999 downloads<\/span>\n\t)\n<\/a>\n<\/div>\n\n<\/div>\n

<\/p>\n

To understand how this works, let us consider the following implementation of complex numbers. The arithmetic operators are overloaded for the Complex<\/tt> type so we can perform operations such as additions, subtractions, and multiplications. <\/p>\n

public struct Complex : IEquatable<Complex>\r\n{\r\n  public static readonly Complex Zero = new Complex(0, 0);\r\n  public static readonly Complex One = new Complex(1, 0);\r\n  public static readonly Complex ImaginaryOne = new Complex(0, 1);\r\n\r\n  public double Real { get; }\r\n  public double Imaginary { get; }\r\n\r\n  public Complex(double r, double i)\r\n  {\r\n     Real = r;\r\n     Imaginary = i;\r\n  }\r\n\r\n  public override string ToString() => $\"{Real}+{Imaginary}i\";\r\n\r\n  public bool Equals(Complex other)\r\n  {\r\n     return Real.Equals(other.Real) && Imaginary.Equals(other.Imaginary);\r\n  }\r\n\r\n  public override bool Equals(object obj)\r\n  {\r\n     Complex other = (Complex)obj;\r\n     return Real.Equals(other.Real) && Imaginary.Equals(other.Imaginary);\r\n  }\r\n\r\n  public override int GetHashCode()\r\n  {\r\n     return Real.GetHashCode() * 13 + Imaginary.GetHashCode();\r\n  }\r\n\r\n  public static Complex operator +(Complex a, Complex b) =>\r\n     new Complex(a.Real + b.Real, a.Imaginary + b.Imaginary);\r\n  public static Complex operator -(Complex a, Complex b) =>\r\n     new Complex(a.Real - b.Real, a.Imaginary - b.Imaginary);\r\n  public static Complex operator *(Complex a, Complex b) =>\r\n     new Complex(a.Real * b.Real - a.Imaginary * b.Imaginary,\r\n                 a.Real * b.Imaginary + a.Imaginary * b.Real);\r\n}<\/pre>\n
For the purpose of this article, we will consider testing the multiplication operator.<\/p>\n
Typically, for testing the multiplication, you would write code as the following:<\/p>\n
[TestMethod]\r\npublic void Test_Multiply()\r\n{\r\n   Assert.AreEqual(new Complex(0, 0),\r\n                   new Complex(1, 2) * new Complex(0, 0));\r\n   Assert.AreEqual(new Complex(1, 2),\r\n                   new Complex(1, 2) * new Complex(1, 0));\r\n   Assert.AreEqual(new Complex(-2, 1),\r\n                   new Complex(1, 2) * new Complex(0, 1));\r\n   Assert.AreEqual(new Complex(-5, 10),\r\n                   new Complex(1, 2) * new Complex(3, 4));\r\n}<\/pre>\n
However, this has the drawback that data is hard coded and the more tests you want to write the more lines like these you need to add. Moreover, every time you want to add new or remove or change existing tests you need to modify the test method.<\/p>\n
The alternative for this is data-driven unit tests with the data fetched from an external data sources. When writing a data-driven unit test you have to do the following:<\/p>\n