[SalesForce] Lead Conversion Trigger Test Failing

I have the following trigger that is working properly

trigger LeadConversionTrigger on Lead (after update) {
for (Lead l : Trigger.new){
    if (checkRecursive.runOnce()){
            // only run if there is an order and an approved certification on the lead
        if (l.Order_Count__c > 0 && l.Certification_Current_State__c == 'Approved'
        && l.Potential_VIP_Customer__c == false) {

            // create an instance of the lead convert object
            Database.LeadConvert lc = new database.LeadConvert();
            lc.setLeadId(l.id);

            // set the status to a converted stage of qualified
            LeadStatus convertStatus = [SELECT Id, MasterLabel FROM LeadStatus 
                                        WHERE IsConverted=true LIMIT 1];
            lc.setConvertedStatus(convertStatus.MasterLabel);

            // log some stuff
            System.debug('### Lead ID = ' + lc.leadid );
            System.debug('### Is Converted = '+ l.IsConverted );
            lc.setDoNotCreateOpportunity(TRUE);         

            Database.LeadConvertResult lcr = Database.convertLead(lc);

            // log some more stuff
            System.debug('### Result = '+ lc );
            system.debug('### Lead conversion result: '+lc );  

            System.assert(lcr.isSuccess());

        }
    }
}       

}

My first test is failing because of the following error:

System.DmlException: ConvertLead failed. First exception on row 0; first error: CANNOT_INSERT_UPDATE_ACTIVATE_ENTITY, There was an error converting the lead. Please resolve the following error and try again:
LeadConversionTrigger: execution of AfterUpdate caused by: System.DmlException: ConvertLead failed. First exception on row 0; first error: CANNOT_UPDATE_CONVERTED_LEAD, This lead was already converted to the contact TestLastName on 02/08/2018.: []
Trigger.LeadConversionTrigger: line 22, column 1: []

Here is the test class:

    @isTest
private class LeadConversionTest {
    static testMethod void successfulConversionTest(){

        Lead objLead = new Lead();
        objLead.Company = 'Test12';
        objLead.Status = 'Open';
        objLead.LastName = 'TestLastName';
        objLead.Potential_VIP_Customer__c = false;
        objLead.Order_Count__c = 2;
        objLead.Certification_Current_State__c = 'Approved';

        insert objLead;

        Database.Leadconvert lc = new Database.Leadconvert();
        lc.setLeadId(objLead.id);
        LeadStatus convertStatus = [select id,MasterLabel from LeadStatus where isConverted=true limit 1];
        lc.setConvertedStatus(convertStatus.MasterLabel);
        Database.LeadConvertResult lcr = Database.convertLead(lc);

        System.assert(objLead.convertedAccountId != null);  
    }
}

If anyone could show me what I'm missing here it would be greatly appreciated.