How to cover POST method in test class in Salesforce?

You can use the following way to cover Post method.

`@isTest
static void testHttpPost() {
// prepare test-data

//As Per Best Practice it is important to instantiate the Rest Context
RestRequest req = new RestRequest();
RestResponse res = new RestResponse();
req.requestURI = '/services/apexrest/Something'; //Request URL
req.httpMethod = 'POST';

RestContext.request = req;
RestContext.response= res;

Test.startTest();
String actual = null;//HttpClass.updateCustomObject();
Test.stopTest();

System.assertEquals('expected value', actual, 'Value is incorrect');
}`