3. Semantic test assertion

Learning objectives

This exercise introduces the Assert.That and related classes.

Intro and motivation

The NUnit test framework and the Unity Test Framework have a series of classes for asserting objects in a way that is closer to natural language. This makes the statements easily readable.

Here are some examples on how to use the semantic assertion classes:

Assert.That(myValue, Is.GreaterThan(20));
Assert.That(str, Does.Contain("a string").And.Contain("something else"));

Here we check that the variable myValue is greater than 20 and then that the string str contains both "a string" and "something else".

The semantic assertion is also known as Constraint Model. Other than It and Does there are multiple other keywords that can be used.

Exercise

In the 3_SemanticTestAssertion sample, there is a class called ValueOutputter, which returns values of different types.

Write tests that assert on the different outputs. It should be verified that:

GetInt() returns 11.
GetString() returns a string that contains the words string and asserted.
GetFloat() returns a value that is around 19.33.

Hints

Asserting on the float might require a check for the value being greater than 19.33 and less than 19.34, as the output is not rational.

Solution

A full solution to the exercise is available in the sample 3_SemanticTestAssertion_Solution.

internal class ValueOutputterTests
{
 [Test]
 public void GivesExpectedInt()
 {
  var outputterUnderTest = new ValueOutputter();

  var number = outputterUnderTest.GetInt();
  
  Assert.That(number, Is.EqualTo(11));
 }
 
 [Test]
 public void GivesExpectedString()
 {
  var outputterUnderTest = new ValueOutputter();

  var str = outputterUnderTest.GetString();
  
  Assert.That(str, Does.Contain("string").And.Contain("asserted"));
 }
 
 [Test]
 public void GivesExpectedFloat()
 {
  var outputterUnderTest = new ValueOutputter();

  var number = outputterUnderTest.GetFloat();
  
  Assert.That(number, Is.GreaterThan(19.33f).And.LessThan(19.34f));
 }
}