Attempt to de-reference a null object when calling class method from Test class

Question

I am trying to write a test method that calls a method in my class to get some configuration data. The method in my class returns a Map. From my test method, when I call the method in my class, I get an error which happens when I call APIService.getSystemSettings();

System.NullPointerException: Attempt to de-reference a null object

My code is below:

  private class APIServiceTest {

    @isTest static void APITest() {
      Map<String,String> envSettings = new Map<String,String>();
      envSettings = APIService.getSystemSettings();
    }

 }

Here is the class which contains the method I am calling:

public class APIService {

  static API_Settings__c apiSettings = API_Settings__c.getValues('apisettings')        
  static Map<String,String> envSettings = new Map<String,String>();

  public static Map<String,String> getSystemSettings() {
   envSettings.put('customerURL', apiSettings.customer_url__c);
  }

}

Most of my methods in APIService are methods annotateded with @Future(Callout=true) so that is why most of the variables are declared as static methods.

I am trying to determine why I am getting this error and what is needed to fix it.

Answer 1

In unit test context, Custom Settings are treated as data (not metadata), and hence are not visible due to test isolation.

Your unit test's setup, whether in your @isTest or an @testSetup method, must construct and insert any Custom Settings records you wish to have available to your test code.

You get a NullPointerException because there is no visible API_Settings__c instance called apisettings; it's null.