How to write a test class for an apex trigger - salesforce

Question

Can someone explain to me how to write a test class for an apex trigger like the following one?
trigger LeadAssignmentTrigger on Broker__c (before insert,before update)
{
List<Broker__c > leadsToUpdate = new List<Broker__c >();
for (Broker__c broker: Trigger.new)
{
if (broker.Referral_ID__c!= NULL)
{
String str = broker.Referral_ID__c;
Integer ln = str.Length();
String likeStr = '%'+str.subString(ln-10, ln-7)+'%'+str.subString(ln-7, ln-4) +'%'+ str.subString(ln-4);
// Find the sales rep for the current zip code
List<User> zip = [select Id from User
where MobilePhone Like : likeStr];
// if you found one
if (zip.size() > 0)
{
//assign the lead owner to the zip code owner
broker.OwnerId = zip[0].Id;
leadsToUpdate.add(broker);
}
else
{
// Throw Error
broker.addError('Invalid Referrel ID');
}
}
}
}
I am new to salesforce.Anyone help me to how to write apex class(test class) for above trigger.
#isTest
private class LeadAssignmentTriggerTest
{
static testMethod void validateHelloWorld()
{
User userObj = new User( Id = UserInfo.getUserId() );
userObj.MobilePhone = '5555555555';
update userObj
test.startTest();
try
{
Broker__c broker = new Broker__c();
broker.Referral_ID__c = '55555555';
broker.City ='New York';
// Add all required field here
insert broker;
}
Catch(Exception ee)
{
}
test.stopTest();
}
}
AccountBrowseExtensionTesttestAccountBrowseSystem.DmlException: Insert failed. First exception on row 0; first error: FIELD_CUSTOM_VALIDATION_EXCEPTION, City is mandatory: []
Stack Trace: Class.AccountBrowseExtensionTest.testAccountBrowse: line 20, column 1
CloseActivityControllerTesttestCloseActivitySystem.DmlException: Insert failed. First exception on row 0; first error: FIELD_CUSTOM_VALIDATION_EXCEPTION, City is mandatory: []
Stack Trace: Class.CloseActivityControllerTest.testCloseActivity: line 13, column 1
changeOwnerControllerTesttestchangeOwnerSystem.DmlException: Insert failed. First exception on row 0; first error: FIELD_CUSTOM_VALIDATION_EXCEPTION, City is mandatory: []
Stack Trace: Class.changeOwnerControllerTest.testchangeOwner: line 20, column 1
cntactsclassTesttestcntactsSystem.DmlException: Insert failed. First exception on row 0; first error: FIELD_CUSTOM_VALIDATION_EXCEPTION, City is mandatory: []
Stack Trace: Class.cntactsclassTest.testcntacts: line 13, column 1
LogACallControllerTesttestLogACallSystem.DmlException: Insert failed. First exception on row 0; first error: FIELD_CUSTOM_VALIDATION_EXCEPTION, City is mandatory: []
Stack Trace: Class.LogACallControllerTest.testLogACall: line 14, column 1
RedirectControllerTesttestRedirectSystem.DmlException: Insert failed. First exception on row 0; first error: FIELD_CUSTOM_VALIDATION_EXCEPTION, City is mandatory: []
Stack Trace: Class.RedirectControllerTest.testRedirect: line 20, column 1
TestAccountSharetestSystem.DmlException: Insert failed. First exception on row 0; first error: FIELD_CUSTOM_VALIDATION_EXCEPTION, Mobile Number is mandatory after Appointment is fixed.: []
Stack Trace: Class.TestAccountShare.test: line 40, column 1

Answer 1

You are writing a trigger for Broker__c on before insert and before update
So since it's a trigger, your code will run every time you insert or update a record.
To write a test class simply create two test methods:
one to insert a Broker__c record
one to update a Broker__c record
Check here on how to create test classes
By the way you should check the best coding practices on how to write a better trigger and handlers here
Edit:
You should also remove the SOQL inside the loop and create a Map with your query outside the for loop