Adding a Test Class

1swfobject.registerObject("clippy.codeblock-0", "9");@isTest 
2private class HelloWorldTestClass {
3    static testMethod void validateHelloWorld() {
4       Book__c b = new Book__c(Name='Behind the Cloud', Price__c=100);
5       System.debug('Price before inserting new book: ' + b.Price__c);
6
7       // Insert book
8       insert b;
9    
10       // Retrieve the new book
11       b = [SELECT Price__c FROM Book__c WHERE Id =:b.Id];
12       System.debug('Price after trigger fired: ' + b.Price__c);
13
14       // Test that the trigger correctly updated the price
15       System.assertEquals(90, b.Price__c);
16    }
17}
18

This class is defined using the @isTest annotation. Classes defined as such can only contain test methods. One advantage to creating a separate class for testing is that classes defined with isTest don't count against your organization limit of 3 MB for all Apex code. You can also add the @isTest annotation to individual methods. For more information, see IsTest Annotation and Understanding Execution Governors and Limits.

The method validateHelloWorld is defined as a testMethod. This means that if any changes are made to the database, they are automatically rolled back when execution completes and you don't have to delete any test data created in the test method.

First the test method creates a new book and inserts it into the database temporarily. The System.debug statement writes the value of the price in the debug log.

1Book__c b = new Book__c(Name='Behind the Cloud', Price__c=100);
2System.debug('Price before inserting new book: ' + b.Price__c);
3
4// Insert book
5insert b;

Once the book is inserted, the code retrieves the newly inserted book, using the ID that was initially assigned to the book when it was inserted, and then logs the new price that the trigger modified:

1// Retrieve the new book
2b = [SELECT Price__c FROM Book__c WHERE Id =:b.Id];
3System.debug('Price after trigger fired: ' + b.Price__c);

When the MyHelloWorld class runs, it updates the Price__c field and reduces its value by 10%. The following line is the actual test, verifying that the method applyDiscount actually ran and produced the expected result:

1// Test that the trigger correctly updated the price
2System.assertEquals(90, b.Price__c);