How to Test ApexRest

BookManager_UnitTest

@isTest
public class BookManager_UnitTest {
    public static testMethod void unitTest_PostMethod(){
        RestRequest request = new RestRequest();
        request.requestURI = '/services/apexrest/v1/BookManagement/';
        request.httpMethod = 'POST';
        
        request.addHeader('Content-Type', 'application/json');
        request.addHeader('Accept', 'application/json');
        //request.addHeader('Authorization', 'Bearer '+Userinfo.getSessionId());
        
        BookManager.BooksInfo bInfo = new BookManager.BooksInfo();
        bInfo.book = new Book__c(Name='test Book', Price__c = 123.98);
        String requestBody = JSON.serialize(bInfo);
        
        request.requestBody = Blob.valueOf(requestBody);
        
        Test.startTest();
        	Book__c book = BookManager.doCreateBook(bInfo);
            System.assertEquals('test Book', book.Name);
        	System.assertNotEquals(null, book.Id);
        Test.stopTest();
    }
    
    public static testMethod void unitTest_GetMethod(){
        Id bookId = createBookRecord();
        RestRequest request = new RestRequest();
        request.requestURI = '/services/apexrest/v1/BookManagement/';
        request.httpMethod = 'GET';
        
        request.addHeader('Content-Type', 'application/json');
        request.addHeader('Accept', 'application/json');
        
        request.addParameter('Id', bookId);
        
        RestContext.request = request;
        
        Test.startTest();
        	Book__c book = BookManager.doGetBook();
            System.assertEquals('Another book', book.Name);
        	System.assertNotEquals(null, book.Id);
        Test.stopTest();
    }
    public static testMethod void unitTest_UpdateMethod(){
        Id bookId = createBookRecord();
        RestRequest request = new RestRequest();
        request.requestURI = '/services/apexrest/v1/BookManagement/';
        request.httpMethod = 'POST';
        
        request.addHeader('Content-Type', 'application/json');
        request.addHeader('Accept', 'application/json');
        //request.addHeader('Authorization', 'Bearer '+Userinfo.getSessionId());        
        request.requestBody = Blob.valueOf('Update book Name');
        request.addParameter('Id', bookId);
        
        RestContext.request = request;
        
        Test.startTest();
        	Book__c book = BookManager.doUpdateBook('Update book Name');
            System.assertEquals('Update book Name', book.Name);
        	System.assertNotEquals(null, book.Id);
        Test.stopTest();
    }
    public static testMethod void unitTest_DeleteMethod(){
        Id bookId = createBookRecord();
        RestRequest request = new RestRequest();
        request.requestURI = '/services/apexrest/v1/BookManagement/';
        request.httpMethod = 'GET';
        
        request.addHeader('Content-Type', 'application/json');
        request.addHeader('Accept', 'application/json');
        
        request.addParameter('Id', bookId);
        
        RestContext.request = request;
        
        Test.startTest();
        	String deletedMessage = BookManager.doDeleteBook();
        	System.assertEquals('Record Deleted!', deletedMessage);
        Test.stopTest();
    }
    
    public static Id createBookRecord(){
       Book__c book = new Book__c(Name ='Another book');
        insert book;
        return book.Id;
    }
}