Assertion in Selenium Webdriver using C#

 

Introduction

Selenium Webdriver would easily automate any scenario on web app with its feature rich API's for web automation. However when we are developing test automation framework we would require to assert on certain steps of the test case that is being automated. The responsibility of  such assertion methods are not part of Selenium Webdriver library and requires us to rely on external assertion frameworks or develop our own methods to able to assert on certain steps.

What is Assertion Library?

Assertion is to verify if the expected behaviour after certain action on application is as expected or correct as per the test step.

A library which provides this functionality without explicitly writing code with condition but by directly calling the supporting function of library which could satisfy the verification condition and also supports different data types or types as variation to same condition.

Examples:

• NUnit.Framework
• Microsoft.VisualStudio.TestTools.UnitTesting
• assert.xunit
• FluentAssertions

Types of Assert Methods?

Assert Methods are broadly classified into below categories. There are many methods in assert class with multiple overloaded variations in implementation. Below is example assertion class categories and simple example of each type. (NUnit example)

Assert Types	About Assert	Assert Syntax
Equality Asserts	Two arguments are equal	Assert.AreEqual( int expected, int actual );
Identity Asserts	Same objects are referenced by the two arguments	Assert.AreSame( object expected, object actual );
Condition Asserts	Tests specific condition	Assert.IsTrue( bool condition );
Comparison Asserts	Tests one object is greater than than another	Assert.Greater( int arg1, int arg2 );
Type Asserts	Assertions about the type of an object	Assert.IsInstanceOfType( Type expected, object actual );
Exception Asserts	Verify that it throws a particular exception	Exception Assert.Throws( Type expectedExceptionType, TestDelegate code );
Utility Methods	Utility methods, Pass(), Fail(), Ignore() and Inconclusive()	Assert.Pass();
String Assert	Examines string values	StringAssert.Contains( string expected, string actual );
Collection Assert	Examining collections	CollectionAssert.AllItemsAreInstancesOfType( IEnumerable collection, Type expectedType );
File Assert	Comparing two files	FileAssert.AreEqual( Stream expected, Stream actual );
Directory Assert	Asserts about file system directories	DirectoryAssert.AreEqual( DirectoryInfo expected, DirectoryInfo actual );

Simillary, there are assert methods available in respective assertion frameworks of MS Test, XUnit and FluentAsserions.

Fluent Assertions:

Fluent assertions are extensive set of assertion methods which supports .Net Framework and are written in TDD, BDD style tests.

For example:

String actual = "AutomationGlance";

actual.Should().StartWith("Automation").And.EndWith("Glance").And.Contain("Au").And.HaveLength(16);

Best Practices of Assertion in UI Test Automation

• Do not forget to add Assert call wherever applicable in a particular test case otherwise the test would always pass.
• Giving a message as argument in Assert statement will make the result analysis easier when assert fails
• There should be at least one assert method per test case, there can be multiple assertions in test case if there are multiple expected results in one manual test case that is automated.
• If one assert fails in a test case then the remaining part after the assert call won't be executed and test will be marked as failed.