nUnit is an open-source unit testing framework for the .NET Framework and Mono. By using nUnit you can test your Services, but also your Controllers, Actions, etc. It was initially ported from JUnit (a Java unit testing framework) and it has been developed and continually rewritten with many new features and support for a wide range of .NET framework versions.

You can learn more about nUnit be navigating to their open source GitHub repository, but which are some must-know helpers that you can use when testing your apps?

nUnit has 5 helper classes:

1. Is
2. Has
3. Contains
4. Does
5. Throws

These helper classes can be used with the constrain model that NUnit offers for better method readability. In the constrained model, the most important method that you can use is the that() method. Inside this method, we specify the expected response which we use to check against the actual response.

But, which are these constrain categories. Constain categories can be divided into eight categories:

1. Comparison
2. String
3. Collection
4. Conditional
5. Compound
6. Directory/File
7. Type/Reference
8. Exceptions

Let us have a look at all these categories and their methods including some examples.

1. Comparison

Comparison category has 5 methods that you can use.

Equal

int result = 5;
Assert.That(result, IsEqualTo(5));

Not Equal

int result = 5;
Assert.That(result, Is.Not.EqualTo(13));

Greater Than

int result = 5;
Assert.That(result, Is.GreaterThan(1));
Assert.That(result, Is.GreaterThanOrEqualTo(5));

Less Than

int result = 5;
Assert.That(result, Is.LessThan(10));
Assert.That(result, Is.LessThanOrEqualTo(5));

Ranges

int result = 5;
Assert.That(result, Is.InRange(1, 10));
Assert.That(result, Is.LessThanOrEqualTo(4, 8));

2. String

Equal / Not Equal

string blogName = "dotnethow";
Assert.That(blogName, Is.EqualTo("dotnethow"));
Assert.That(blogName, Is.Not.EqualTo("dotnethow-not"));

Equal with Ignore Case

string blogName = "dotnethow";
Assert.That(blogName, Is.EqualTo("dotNEThow").IgnoreCase);

Contains substring

string blogName = "dotnethow";
Assert.That(blogName, Does.Contain("net"));
Assert.That(blogName, Does.Not.Contain("NET").IgnoreCase);

Empty

string blogName = "dotnethow"; string blogNameEmpty="";
Assert.That(blogNameEmpty, Is.Empty);
Assert.That(blogName, Is.Not.Empty);

Starts/Ends With

string blogName = "dotnethow";
Assert.That(blogName, Does.StartWith("dot"));
Assert.That(blogName, Does.Not.StartWith("net"));

Assert.That(blogName, Does.EndWith("how"));
Assert.That(blogName, Does.Not.EndWith("net"));

Regex/Match

string blogName = "dotnethow";
Assert.That(blogName, Does.Match("d*w"));
Assert.That(blogName, Does.Not.Match("m*n"));

3. Collection

Not Null

int[] array = new int[]{1, 2, 3, 4, 5, 6, 7, 8};
Assert.That(array, Is.All.Not.Null);

All Greater Than

int[] array = new int[]{1, 2, 3, 4, 5, 6, 7, 8};
Assert.That(array, Is.All.GreaterThan(0));

All Less Than

int[] array = new int[]{1, 2, 3, 4, 5, 6, 7, 8};
Assert.That(array, Is.All.LessThan(0));

Instance Of

int[] array = new int[]{1, 2, 3, 4, 5, 6, 7, 8};
Assert.That(array, Is.All.InstanceOf<Int32>());

Empty

int[] array = new int[]{1, 2, 3, 4, 5, 6, 7, 8};
Assert.That(array, Is.Empty);
Assert.That(array, Is.Not.Empty);

Number of items

int[] array = new int[]{1, 2, 3, 4, 5, 6, 7, 8};
Assert.That(array, Has.Exactly(8).Items);

Unique Items

int[] array = new int[]{1, 2, 3, 4, 5, 6, 7, 8};
Assert.That(array, Is.Unique);

Contains Item

int[] array = new int[]{1, 2, 3, 4, 5, 6, 7, 8};
Assert.That(array, Contains.Item(4));

Ordered in Ascending/Descending

int[] arrayAscending = new int[]{1, 2, 3, 4, 5, 6, 7, 8};
Assert.That(arrayAscending , Is.Ordered.Ascending);

int[] arrayDescending = new int[]{4, 3, 1};
Assert.That(arrayDescending , Is.Ordered.Descending);

By Single Property/Multiple Properties

List<Book> books = new List<Book>();
books.Add(new Book(){ Title = "Book 1", NrOfPages = 450  });
books.Add(new Book(){ Title = "Book 2", NrOfPages = 350 });
books.Add(new Book(){ Title = "Book 3", NrOfPages = 150 });

Assert.That(books, Is.Ordered.Ascending.By("Title"));
Assert.That(books, Is.Ordered.Descending.By("Title"));

Assert.That(books, Is.Ordered.Ascending.By("Title").Then.Descending.By("NrOfPages"));

Subset/SuperSet

int[] array1 = new int[]{1, 2, 3, 4, 5, 6, 7, 8};
int[] array2 = new int[]{4, 5, 6};

Assert.That(array2 , Is.SubsetOf(array1));
Assert.That(array1 , Is.SupersetOf(array2));

4. Conditional

Null

int[] array = new int[]{4, 5, 6};

Assert.That(array, Is.Null);
Assert.That(array, Is.Not.Null);

Boolean

int[] array = new int[]{4, 5, 6};
bool result = array.Length > 1;

Assert.That(result, Is.True);
Assert.That(result, Is.False);

Empty

int[] array = new int[]{4, 5, 6};

Assert.That(array, Is.Empty);

5. Compound

AND

int result = 10;

Assert.That(result, Is.GreaterThan(5).And.LessThan(20));

OR

int result = 10;

Assert.That(result, Is.GreaterThan(5).Or.LessThan(20));

NOT

int result = 10;

Assert.That(result, Is.Not.EqualTo(5));

6. Directory/File

File/Directory Exists

Assert.That(new FileInfo(filePath), Does.Exist);
Assert.That(new FileInfo(filePath), Does.Not.Exist);

Assert.That(new DirectoryInfo(directoryPath), Does.Exist);
Assert.That(new DirectoryInfo(directoryPath), Does.Not.Exist);

Same Path

Assert.That(filePath, Is.SamePath(@"c:\docs\folder\filehere").IgnoreCase);

Directory Is Empty

Assert.That(new DirectoryInfo(directoryPath), Is.Empty);

7. Type/Reference

Instance

IBook book = new Book();

Assert.That(book, Is.InstanceOf<IBook>());
Assert.That(book, Is.Not.InstanceOf<string>());

Exact Same Type

IBook book = new Book();

Assert.That(book, Is.TypeOf<Book>());

Assingable

IBook book = new Book();

Assert.That(book, Is.AssignableTo<Book>());

8. Exceptions

Is Exception Thrown

var booksService = new BooksService();

Assert.That(books.GetAllBooks(), Throws.Exception);

Expected/Same Type Exception

var booksService = new BooksService();

Assert.That(books.GetBookById(), Throws.Exception.TypeOf<ArgumentException>());

Exception Message

var booksService = new BooksService();

Assert.That(() => booksService.Add(null), Throws.Exception.TypeOf<ArgumentNullException>()
                .With.Message.EqualTo($"Please, provide a book title"));