Trouble writing my first APEX test class

Question

I'm very new to APEX and I'm trying to implement a feature where new contacts added contain a field called Company__c. From this field, a lookup is done to find the Account by the same name, and then associates the two.

My code is as follows:

trigger associateWithAccount on Contact (before insert) {
    if(Trigger.isBefore){
        if(Trigger.isInsert){
                Map<String, String> extMap = new Map<String, String>();
                Set<String> extIdSet = new Set<String>();
                for(Contact c : Trigger.new){
                    extIdSet.add(c.Company__c);
                }
            for(Account a : [select Id, Name from Account where Name IN :extIdSet]){
                extMap.put(a.Id, a.Name);
            }
            for(Contact c : Trigger.new){
                c.AccountID = extMap.get(c.Company__c);
            }
        }
    }
}

I have no idea if that works, I just know it doesn't give me any errors. However, I have no idea how to write the test class to attain the necessary code coverage, nor how to link the trigger and the test class. Any help?

This is my test code so far, but I keep getting an error about the Account__r (which I've never used before):

@isTest
private class TestAssociateWithAccount {
    static testMethod void myUnitTest() {
        Account testAccount = new Account(AccountID='98765', Account='test123');
        insert testAccount; 
        Test.startTest();
        Contact testContact = new Contact(Company__c='test123');
        insert testContact;
        Test.stopTest();
        Contact result = [select AccountID, Account__r.Name, Account__r.Account from Contact where Company__c = 'test123' limit 1];
        system.assertEquals(testAccount.AccountID, result.Contact__c);
    }
}

Thanks!

Edit: Current Trigger Code:

trigger associateWithAccount on Contact (before insert) {
    Map<String, String> extMap = new Map<String, String>();

    for(Contact c : Trigger.new){
        extMap.put(c.Company__c,null);
    }

    for(Account a : [select Id, Name from Account where Name IN :extMap.keySet()]){
        extMap.put(a.Name,a.ID);
    }
    for(Contact c : Trigger.new){
       ID tmp = extMap.get(c.Company__c); 
       if(tmp != null)
          c.AccountID = tmp;
    }
}

Current Test Class Code:

@isTest
private class TestAssociateWithAccount {
    static testMethod void myUnitTest() {
        Account testAccount = new Account(ID='5003000000D8cuI', Name='test123');
        insert testAccount; 
        Test.startTest();
        Contact testContact = new Contact(Company__c='test123');
        insert testContact;
        Test.stopTest();
         Contact result = [select AccountID, Account.Name from Contact where Company__c = 'test123' limit 1];
        system.assertEquals(testAccount.ID, result.AccountID);
    }
}

Answer 1

Not a bad start for your first test class.

believe it or not you seem to understand what A LOT of people do not.

Now to the problem....

Standard fields do NOT have __c or __r appended to them

so the query needs to be:

Contact result = [select AccountID, Account.Name from Contact where Company__c = 'test123' limit 1];
system.assertEquals(testAccount.ID, result.AccountID);

Thinking through this logically:

You are querying for the contact and want to validate the Account related to it is the same as the testaccount...

So you need to grab the same fields that you are setting in your trigger, namely the AccountID field.

Now on to your trigger:

1. You do not need the first two IF statements. Since the scope of the trigger is only Before Insert it will only fire for that condition. You only need the first two IF statements if the scope of the trigger covers multiple conditions

2. The second part of your trigger will not work because you are assigning a Name to an accountID. If the contact__c is a lookup then you can simply copy the ID

Here are two versions

If Company__c is a lookup to account

trigger associateWithAccount on Contact (before insert) {
                for(Contact c : Trigger.new){
                    c.AccountID = c.Company__c;
                }
}

If Company__c is a String Name of an Account

trigger associateWithAccount on Contact (before insert) {
    Map<String, String> extMap = new Map<String, String>();

    for(Contact c : Trigger.new){
        extMap.put(c.Company__c,null);
    }

    for(Account a : [select Id, Name from Account where Name IN :extMap.keySet()]){
        extMap.put(a.Name,a.ID);
    }
    for(Contact c : Trigger.new){
       c.AccountID = extMap.get(c.Company__c); 
    }
}