webservice static void RESTApiToAccount(id AccountId)
{
String clientId = '3MVG9YDQS5WtC11p0izGLTFFxnJa365Xd9WpNGN1oZPe1ArfQML4Q8EKN8ye3qF4m7iCVPWas1LV1OVCFd9oO';
String clientSecret = '4032474715821060338';
String username = '';
String password = '';
String reqbody = 'grant_type=password&client_id='+clientId+'&client_secret='+clientSecret+'&username='+username+'&password='+password;
Http h = new Http();
HttpRequest req = new HttpRequest();
req.setBody(reqbody);
req.setMethod('POST');
req.setEndpoint('https://ap4.salesforce.com/services/oauth2/token');
HttpResponse res = h.send(req);
SendAccountUsingRESTAPI resp1 = (SendAccountUsingRESTAPI)JSON.deserialize(res.getbody(),SendAccountUsingRESTAPI.class);
system.debug('@@@@access_token@@'+res.getbody() );
String accessToken;
accessToken = resp1.access_token;
if(accessToken != null)
{
String endPoint = 'https://ap4.salesforce.com/services/apexrest/Account';
JSONGenerator gen = JSON.createGenerator(true);
Account a=[select id,name,website from account where id=:AccountId];
gen.writeStartObject();
gen.writeStringField('name', a.name);
gen.writeStringField('id', a.id);
gen.writeStringField('website', a.website);
String s=gen.getasString();
Http h2 = new Http();
HttpRequest req1 = new HttpRequest();
req1.setHeader('Authorization','Bearer ' + accessToken);
req1.setHeader('Content-Type','application/json');
req1.setHeader('accept','application/json');
req1.setBody(s);
system.debug('sumaiyaaaaaa'+req1.getbody());
req1.setMethod('POST');
req1.setEndpoint(endPoint);
HttpResponse res1 = h2.send(req1);
String trimmedResponse = res1.getBody();
system.debug('sasasasa'+res1);
system.debug('@@@RESPONSE@@'+trimmedResponse);
JSONParser parser = JSON.createParser(res1.getBody());
}

@isTest
static void myTest() { // Set mock callout class
    Test.startTest();

    Test.setMock(HttpCalloutMock.class, new MockHttpResponseGenerator());

    Account a=new account();
    a.name='test';
    a.website='www.test.com';

    SendAccountUsingRESTAPI.RESTApiToAccount(a.id);

    Test.StopTest();
}

@isTest
public class MockHttpResponseGenerator implements HttpCalloutMock {
    // Implement this interface method
    public HTTPResponse respond(HTTPRequest req) {
             String endpoint = req.getEndpoint();
        if ( endpoint.contains('oauth2/token') ) {
            return buildOAuthResponse( req );
        } else if ( endpoint.contains('/services/apexrest/Account') ) {
            return buildShortenResponse( req );
        }
        return null;
    }
  private HttpResponse buildOAuthResponse( HttpRequest req ) {
        HttpResponse res = new HttpResponse();
        res.setBody('123');
        res.setStatusCode(200);
        return res;
    }
    private HttpResponse buildShortenResponse( HttpRequest req ) {

        // Create a fake response
        HttpResponse res = new HttpResponse();
        res.setHeader('Content-Type', 'application/json');
        res.setBody('{"foo":"bar"}');
        res.setStatusCode(200);
        return res;
    }
}