I am using a Marketing Automation Tool that will Create a Contact (not using Leads), I created a trigger to create Account (FirstName LastName and - Account, I get error and trigger and test class below:

Error Message System.ListException: List index out of bounds: 0
Stack Trace Class.CreateAccountFromContact_UnitTest.runTest: line 14, column 1

trigger CreateAccountFromContact on Contact (before insert) {
//Collect list of contacts being inserted without an account
    List<Contact> needAccounts = new List<Contact>();
    for (Contact c : trigger.new) {
        if (String.isBlank(c.accountid)) {
            needAccounts.add(c);
        }
    }
   
    if (needAccounts.size() > 0) {
        List<Account> newAccounts = new List<Account>();
        Map<String,Contact> contactsByNameKeys = new Map<String,Contact>();
        //Create account for each contact
        for (Contact c : needAccounts) {
            String accountName = c.firstname + ' ' + c.lastname + ' ' + ' - Account ';
            contactsByNameKeys.put(accountName,c);
            Account a = new Account(name=accountName);
            newAccounts.add(a);
        }
        insert newAccounts;
       
              
  }     
}
 
@isTest
public with sharing class CreateAccountFromContact_UnitTest {
    @isTest
    public static void runTest(){
        String firstname = 'first';
        String lastname = 'last';
               
        //Create contact
        Contact c = new Contact(firstname=firstname, lastname=lastname);
        insert c;
        
        //Verify account
        c = [select id, accountid, firstname, lastname from Contact where id =:c.Id][0];
        Account a = [select id, name from Account where id = :c.accountId][0];
        
        system.assertEquals(firstname + ' ' + lastname + ' ' + ' - Account ', a.name);
        
        
    }
}

I am using a Marketing Automation Tool that will Create a Contact (not using Leads), I created a trigger to create Account (FirstName LastName and - Account, I get error and trigger and test class below:

Error Message System.ListException: List index out of bounds: 0
Stack Trace Class.CreateAccountFromContact_UnitTest.runTest: line 14, column 1

trigger CreateAccountFromContact on Contact (before insert) {
//Collect list of contacts being inserted without an account
    List<Contact> needAccounts = new List<Contact>();
    for (Contact c : trigger.new) {
        if (String.isBlank(c.accountid)) {
            needAccounts.add(c);
        }
    }
   
    if (needAccounts.size() > 0) {
        List<Account> newAccounts = new List<Account>();
        Map<String,Contact> contactsByNameKeys = new Map<String,Contact>();
        //Create account for each contact
        for (Contact c : needAccounts) {
            String accountName = c.firstname + ' ' + c.lastname + ' ' + ' - Account ';
            contactsByNameKeys.put(accountName,c);
            Account a = new Account(name=accountName);
            newAccounts.add(a);
        }
        insert newAccounts;
       
              
  }     
}
 
@isTest
public with sharing class CreateAccountFromContact_UnitTest {
    @isTest
    public static void runTest(){
        String firstname = 'first';
        String lastname = 'last';
               
        //Create contact
        Contact c = new Contact(firstname=firstname, lastname=lastname);
        insert c;
        
        //Verify account
        c = [select id, accountid, firstname, lastname from Contact where id =:c.Id][0];
        Account a = [select id, name from Account where id = :c.accountId][0];
        
        system.assertEquals(firstname + ' ' + lastname + ' ' + ' - Account ', a.name);
        
        
    }
}