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3. Semantic test assertion

Use Assert.That to test whether conditions are true.
Read time 2 minutesLast updated 13 days ago

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)); }}

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