In this recipe, you declared that the TestOnePlusOneEqualsTwo() method in the SimpleTester.cs C# script class is a test method. When executing this test method, Unity Test Runner executes each statement in sequence, so variables n1, n2, and expectedResult are set, then the calculation of 1 + 1 is stored in the variable result, and finally (the most important bit), we make an assertion of what should be true after executing that code. Our assertion states that the value of the expectedResult variable should be equal to the value of the variable result.
If the assertion is true, the test passed; otherwise, it failed. Generally, as programmers, we expect our code to pass, so we inspect each fail very carefully, first to see whether we have an obvious error, then perhaps to check whether the test itself is correct (especially if it's a new test), and then to begin to debug and understand why our code behaved in such a way that it...