//Controller Class
Please Any one Help
Pardot_Credential_Setting__c is Custom Setting
public class pardotActivityController{

        public static Pardot_Credential_Setting__c customSetting(){
            Pardot_Credential_Setting__c objSetting = Pardot_Credential_Setting__c.getValues('Pardot Access');
            if(objSetting != null && objSetting.Sync_disabled__c == false){
                return objSetting;
            }
            return null;
        }
        public static String authMethod(){
            
            Pardot_Credential_Setting__c objSetting = customSetting();

            if(objSetting != null){    <----Not Covering -------->
                String email = objSetting.Pardot_Email__c;
                String password = objSetting.Pardot_Password__c;
                String userKey = objSetting.User_Api_Key__c;

                HttpRequest req = new HttpRequest();
                req.setEndpoint( objSetting.Pardot_BaseUrl__c+'/api/login/version/4' );
                req.setMethod( 'POST' );
                req.setBody( 'email=' + email + '&password=' + password + '&user_key=' + userKey );

                HttpResponse res = new Http().send( req );

                System.debug('>>>>>>>>res'+ res );
                System.debug('>>>>>>>>>res.getStatus()'+ res.getStatus() );
                System.debug('>>>>>>res.getBody()'+ res.getBody() );

                String response = res.getBody();
                
                Integer startIdx;
                Integer endIdx;
                String apiKey;
                if(response.contains('<api_key>')){
                    startIdx = response.indexOf( '<api_key>' ) + 9;
                    endIdx = response.indexOf( '</api_key>' );
                    apiKey = response.substring( startIdx, endIdx );
                    System.debug( '>>>>>>>apiKey'+ apiKey );
                    return apiKey;
                }
            }
            
            return null;
        }
}

<------Test class------->
 static Testmethod void authMethodTest(){ 
        Pardot_Credential_Setting__c objSetting = New Pardot_Credential_Setting__c();
         objSetting.Name = 'Test';
         objSetting.Pardot_Email__c = 'abc@gmail.com';
         objSetting.User_Api_Key__c = '<api_key>';
         objSetting.Pardot_BaseUrl__c = 'https://pi.pardot.com/api/login/version/4';
         objSetting.Pardot_Password__c = 'test12';
         objSetting.Sync_disabled__c = false;
         insert objsetting;
        	Test.setMock(HttpCalloutMock.class, new MockHttpResponseGenerator());
        	test.startTest();
        		pardotActivityController.authMethod();
        	test.stopTest();
    	}
 public class MockHttpResponseGenerator implements HttpCalloutMock{ //Http callout class for authmothod
            public HTTPResponse respond(HTTPRequest req){               
            String json=        '{'+
            '        "EMail": "leadsscotia@culliganwaterco.com",'+
            '        "Password": "<api_key>,'+
            '        "Userkey": "</api_key>",'+
            '}';
                   
            	System.assertEquals('https://pi.pardot.com/api/login/version/4', req.getEndpoint());
            	System.assertEquals('POST', req.getMethod());
                
                //make a fake responce
                 HttpResponse res = new HttpResponse();
                 res.setBody(json);
                 res.setStatusCode(200);
                 return res;
            }
        }