I have a simple trigger on opportunity that populates a primary contact on the opportunity from opportunity contact roles.

The test class is getting 19/20 coverage - with the last missing line being a Map.put used to populate a map used to save opportunity id, contact id. The test class tests that this is working properly - I'm not sure what I may be missing to get coverage.

The Trigger:

// Built by Will Craig 4.25.2019
//
// Trigger for initiating all classes for Opportunity.

trigger Opportunity on Opportunity (before insert, before update, after insert, after update) {

    // Routing for before triggers.
    if(Trigger.isBefore){
        
        if(Trigger.isUpdate){

            opportunityPrimaryContact.PrimaryContactProcessor(Trigger.new, Trigger.oldMap);

        }else if(Trigger.isInsert){

            opportunityPrimaryContact.PrimaryContactProcessor(Trigger.new);

        }

    } else if(Trigger.isAfter){

        // After trigger responses

    }

}

The Class:

public class opportunityPrimaryContact {
    
    // Method for handling inserts
    public static void PrimaryContactProcessor(List<Opportunity> Opportunities) {

        // Create a map for use when updating Primary_Contact__c on Opportunties
        Map<Id,Id> pocrMap = new Map<Id,Id>();
        
        // Create a set of OpportunityIds for use in the OCR query.
        Set<Id> oppidSet = new Set<Id>();
        for(Opportunity opp : Opportunities){
            oppidSet.add(opp.id);
        }

        // Retrieve primary OCRs and populate a map for retrieving them by OpportunityId
        List<OpportunityContactRole> ocrs = [SELECT ContactId,OpportunityId FROM OpportunityContactRole WHERE OpportunityId IN: oppidSet AND IsPrimary = true];
        for(OpportunityContactRole ocr : ocrs){
            pocrMap.put(ocr.OpportunityId,ocr.ContactId);
        }

        // Iterate through opportunities and set Primary_Contact__c, leveraging pocrMap.
        for(Opportunity opp : Opportunities){
            opp.Primary_Contact__c = pocrMap.get(opp.Id);
        }

        // Updates not required in before triggers.

    }

    // Method for handling updates (via overload)
    public static void PrimaryContactProcessor(List<Opportunity> Opportunities, Map<ID,sObject> TriggerOldMap) {

        // Create a map for use when updating Primary_Contact__c on Opportunties
        Map<Id,Id> pocrMap = new Map<Id,Id>();
        
        // Create a set of OpportunityIds for use in the OCR query.
        Set<Id> oppidSet = new Set<Id>();
        for(Opportunity opp : Opportunities){
            oppidSet.add(opp.id);
        }

        // Retrieve primary OCRs and populate a map for retrieving them by OpportunityId
        List<OpportunityContactRole> ocrs = [SELECT ContactId,OpportunityId FROM OpportunityContactRole WHERE OpportunityId IN: oppidSet AND IsPrimary = true];
        for(OpportunityContactRole ocr : ocrs){
   // line below is what is not covered.         pocrMap.put(ocr.OpportunityId,ocr.ContactId);
        }


        // Iterate through opportunities and set Primary_Contact__c, leveraging pocrMap.
        for(Opportunity opp : Opportunities){
            opp.Primary_Contact__c = pocrMap.get(opp.Id);
        }

        // Updates not required in before triggers.

    }

}

Test Class:

@IsTest
public class opportunityPrimaryContact_TEST {
    
    @IsTest
    private static void create_TEST() {

        Test.StartTest();

        User u = new User();
        u.ProfileId = [SELECT Id FROM Profile WHERE Name = 'Standard User'].Id;
        u.LastName = 'last';
        u.Email = 'test@test.com ';
        u.Username = 'test@test.com.' + System.currentTimeMillis();
        u.CompanyName = 'TEST';
        u.Title = 'title';
        u.Alias = 'alias';
        u.TimeZoneSidKey = 'America/Los_Angeles';
        u.EmailEncodingKey = 'UTF-8';
        u.LanguageLocaleKey = 'en_US';
        u.LocaleSidKey = 'en_US';

        Insert u;

        Account acc = new Account();
        acc.Name = 'Test Account';
        acc.ownerid = u.id;

        Opportunity opp = new Opportunity();
        opp.Name = 'Test Opportunity';
        opp.StageName = 'Target';
        opp.CloseDate = Date.Today();
        opp.ownerid = u.id;

        Insert opp;

        Contact c1 = new Contact();
        c1.Firstname = 'Test1First';
        c1.Lastname = 'Test1Last';
        c1.AccountId = acc.id;

        Insert c1;

        OpportunityContactRole ocr1 = new OpportunityContactRole();
        ocr1.ContactId = c1.id;
        ocr1.OpportunityId = opp.id;
        ocr1.IsPrimary = true;
        ocr1.Role = 'Decision Maker';

        Insert ocr1;

        Contact c2 = new Contact();
        c2.Firstname = 'Test2First';
        c2.Lastname = 'Test2Last';
        c2.AccountId = acc.id;

        Insert c2;

        OpportunityContactRole ocr2 = new OpportunityContactRole();
        ocr2.ContactId = c2.id;
        ocr2.OpportunityId = opp.id;
        ocr2.IsPrimary = false;
        ocr2.Role = 'Decision Maker';
        
        Insert ocr2;

        Update opp;
        
        Test.StopTest();

        OpportunityContactRole ocr = [SELECT Id,
                                        ContactId,Contact.Name,OpportunityId 
                                        FROM OpportunityContactRole 
                                        WHERE OpportunityId =: opp.id 
                                        AND IsPrimary = true
                                        ];

        

        Opportunity oppupdated = [SELECT Id,Primary_Contact__c from Opportunity WHERE ID =: opp.id];

        System.debug(ocr);
        System.debug(opp.Primary_Contact__c);
        System.assertEquals(ocr.ContactId,oppupdated.Primary_Contact__c);
        
    }

}