Both are used in Test Class for “Positive Case Testing” and “Negative Case Testing” with single and multiple records.
System Class
Let’s use System.assert and System.assertEquals to do the testing in sample Negative Test Class:
static testMethod void runNegativeTestCases(){
User u3 = [select id from User where alias='tuser'];
System.RunAs(u3)
{
System.debug('Inserting a record with 501 miles... (negative test case)');
Mileage__c testMiles3 = new Mileage__c( Miles__c = 501, Date__c = System.today() );
try{
insert testMiles3;
}catch (DmlException e){
//Assert Error Message
System.assert( e.getMessage().contains('Insert failed. First exception on ' +'row 0; first error:FIELD_CUSTOM_VALIDATION_EXCEPTION,'+'Mileage request exceeds daily limit(500): [Miles__c]'),e.getMessage() );
//Assert field
System.assertEquals(Mileage__c.Miles__c, e.getDmlFields(0)[0]);
//Assert Status Code
System.assertEquals('FIELD_CUSTOM_VALIDATION_EXCEPTION' , e.getDmlStatusCode(0) );
} //catch
} //RunAs(u3)000382121

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