Assertion in Selenium is used for asserting the given input value with the content or value available on the web-page. If the given value with the value on the web-page matches then we will return the true value otherwise we will return false.
If an assertion fails, the method call does not return and an error is reported. If a test contains multiple assertions, any that follow the one that failed will not be executed. For this reason, it's usually best to try for one assertion per test.
Each method may be called without a message, with a simple text message or with a message and arguments. In the last case the message is formatted using the provided text and arguments.
Two Models
Before NUnit 2.4, a separate method of the Assert class was used for each different assertion. We call this the classic model. It continues to be supported in NUnit, since many people prefer it.
Beginning with NUnit 2.4, a new constraint-based model is being introduced. This approach uses a single method of the Assert class for all assertions, passing a constraint object that specifies the test to be performed.
This constraint-based model is now used internally by NUnit for all assertions. The methods of the classic approach have been re-implemented on top of this new model.
Classic Assert Model
The classic Assert model uses a separate method to express each individual assertion of which it is capable.
example: StringAssert.AreEqualIgnoringCase( "Hello", myString );
The Assert class provides the most commonly used assertions. For convenience of presentation, we group Assert methods as follows:
Beyond the basic facilities of Assert, additional assertions are provided by the following classes:
Constraint-Based Assert Model
The constraint-based Assert model uses a single method of the Assert class for all assertions. The logic necessary to carry out each assertion is embedded in the constraint object passed as the second parameter to that method.
Using this model, all assertions are made using one of the forms of the Assert.That() method, which has a number of overloads.
Use below link For Type of Constraint-Based Assert Model
