Executable Tutorial: API Testing using RestSharp And SpecFlow

By: Megha Gangwal(gangwal@kth.se), MD Rezaul Hasan(mrhasa@kth.se)


The learning objective of this tutorial is:

  • At the end of the tutorial, the learner must be able to understand the basic concepts of the RestSharp & SpecFlow.
  • Learners should be able to set up the RestSharp and SpecFlow on the .Net Core project for API Testing.

This tutorial will take approximately 30–40 min depending on the learner’s knowledge and installed software.

Before we start the tutorial, let us ask ourselves a couple of questions,

  • Why do we need automated testing?
  • Why do we need RestSharp?
  • What is the use of SpecFlow?

There are many advantages or benefits of automated testing, some of them are:

  • It helps in finding the bug early in the development phase, resulting in an increase in efficiency
  • Automated Testing helps in the reduction of manual errors and omissions.
  • Automated Testing improves the traceability of requirements across multiple systems, thus reducing the effort in error detection and maintenance of the systems

Due to these advantages, the industry has adopted automated testing to a great degree.


RestSharp is an open-source HTTP client library. It is one of the most used libraries for the Rest API Testing in .Net and .Net Core.

Asynchronous request handling is a key requirement for development on the Microsoft platform. RestSharp supports both synchronous as well as asynchronous requests.

The RestSharp also allows configuring different parts of HTTP call requests, which provides greater flexibility to developers to customize and test. However, it does not support API calls over HTTP/2.

It also supports inbuilt serialization and deserialization and various authentication methods.

Overall RestSharp is a constantly updated open-source library, which provides an easy way to test .net-based applications.


Specflow is an open-source testing framework hosted on GitHub. It supports Behavior Design Development (BDD) practices in .NET. It uses Gherkin syntax to write the test cases and we used cucumber extension for syntax highlighting as well as for basic snippets support. Some of the key concepts used in SpecFlow are

Feature File — It is written in plain text. It defines the test suite in terms of features and contains the actual tests which are called Scenarios.

  • Feature — Feature states the goal for the Feature File. When the Feature File is complete, a tag is included at this level so that all of the test Scenarios contained within the file can be run from a single command
  • Scenario — Individual tests are defined by “Scenario:” followed by a unique name. It defines the expected behavior of the application under test. The first line states the goal of the given Scenario. The subsequent lines define the steps needed to complete the test. There are the following commands reserved by Specflow to define the steps

Given: Used for describing a set of pre-conditions for the scenario

When: Used for describing an action or execution step.

Then: Used for describing the outcome of the scenario and essentially where the validations should be placed in

SpecFlow has a number of key features such as:

1. It completely integrates with Visual Studio (VS) and utilizes VS IDE capabilities

2. It gives complete VS debugger support, which helps in setting the breakpoints on Given/ When/Then lines in .feature files and step through their execution. y

3. StepFlow supports step definitions in any .NET language.

4. SpecFlow feature files comply with an NUnit test assembly. It can be used by an NUnit-compatible test runner or existing CI infrastructure to run the specifications with no additional configuration

Essential Installations:

To do API Testing using RestSharp And SpecFlow on the Linux platform following installations are needed.

  1. Visual Studio Code(vscode) installation.
  2. Install .Net Core SDK
  3. Install .Net Core runtime
  4. Install NuGet package manager extension
  5. Install C# extension
  6. Install Cucumber
  7. Install Gherkin Indent
  8. Install .Net Core Test Explorer
  9. Install json-server
  10. Install RestSharp
  11. Install SpecFlow
  12. Installations of supporting packages

How to install vscode:

Follow the following steps

  1. To download vscode on the Linux platform, please click on this link
  2. After Link has been opened, select the file corresponding to your operating system to download or you can just click on the download option it will automatically download the file corresponding to your operating system. We have selected the .deb extension file for our Linux system.
  3. To install, use the following instructions: Go to your download folder and open your terminal from that folder, then run the command below with the downloaded file name.

Or you can install it from ubuntu software.

Installing .Net Core SDK

  1. Open the terminal window and then execute the following commands:

You could see the following scenario on your terminal

Installing .Net Core runtime

.NET Core Runtime is required for the system, where you only need to run the application. To install Dotnet core runtime on Ubuntu 18.04 Linux system, execute the following commands:

Install NuGet package manager extension

Open visual studio code from your terminal by using the command :

Now you could see the visual studio code IDE opened. On the left side of the IDE, you can find an extension symbol which is pointed by a red arrow in the snapshot. Click on the extension, you will see the generated window as shown below and search for NuGet package manager.

Click on the install button(We have already installed so that’s why you can see uninstall option). In this way, your NuGet package got installed.

Install C# extension

Now in the opened extension search engine, search for c#. Select C# V1.23.12 and click on the install option.

Install Cucumber

In the opened extension search engine, search for Cucumber. Select Cucumber and click on the install option.

Install Gherkin Indent

In the opened extension search engine, search for Gherkin Indent. Select Gherkin Indent and click on the install option.

Install .Net Core Test Explorer

In the opened extension search engine, search for .Net core Test Explorer. You can see like below. Select .Net core Test Explorer and click on the install option.

Install json-server

  1. Nodejs installation for npm
  • Download the installer from NodeJS WebSite according to your operating system.
  • Run the installer.
  • Follow the installer steps, agree on the license agreement and click the next button.

Or, run the below command

To verify Nodejs installation is correct, type

on your terminal window, you will enter into a node terminal like this:

Exit from the terminal by pressing Ctrl + c and again open the new terminal window, type,

to check npm commands are executing or not.

Great! You have successfully installed npm.

2. To install json server: Run this command on the terminal window

3. Create a folder called restsharpSpecFlow on your desktop and inside that folder Create db.json file Code: Paste this code inside the db.json file and save it:

On the terminal window go to your newly created folder and execute the following command to run json-server.

Now if you go to the link, you’ll get a response link below

Shutdown the json-server from the terminal by pressing Ctrl+c

Install RestSharp

Open the terminal through the folder restsharpSpecFlow that you have created for the db.json file.

Execute the following command which will create an NUnit project.

It will create 3 files: obj folder, UnitTest1.cs,and restsharpSpecFlow.csproj

restsharpSpecFlow.csproj file will look like this:

Now let’s install RestSharp: The command for installing RestSharp:

Install SpecFlow

The command for installing SpecFlow:

Installations of supporting packages

To read json file we need this package which helps RestSharp to deserialize received data.

For connecting with the NUnit test case and SpecFlow run this command

This MSBuild package enables the code-behind file generation at build time.

Also, run the below command for avoiding the NUnit version issue:

After installing above all packages the restsharpSpecFlow.csproj file will look like this:

Execution of the tutorial: Once you complete the installations, then follow the steps below:

(A) RestSharp Integration

(B) SpecFlow Integration

Let’s do RestSharp Integration first

(A) RestSharp Integration

  1. Open the vscode through the terminal from the already created folder restsharpSpecFlow by the following command

You can see three files are present there: obj folder, UnitTest1.cs, and restsharpSpecFlow.csproj

2. Open UnitTest1.cs file

3. Now first of all build the project through the vscode terminal by using the command

4. Now import the following packages in the UnitTest1.cs file:


5. Do the following changes inside the public class Tests of the UnitTest1.cs file

Make sure that all double quotes (“ ”)are correctly used as C# syntex.

Let’s understand the code in detail:

5.1 Creating Client Connection:

Creation of the RestClient opens the browser and gets it ready to call any server using a URL. In our scenario, RestClient initializes a client with the specified root address.

5.2 Creating Request for GET method:

Now our Client connection is established, so the client is ready to send requests to the server. Here, RestRequest class creates HTTP Requests to the specified URL. RestRequest class supports different HTTP methods like GET, POST, etc.

Here we are using the GET method to retrieve the information corresponding to attribute “postid”

5.3 Executing Request on the Server for GET method:

Execute method is used to send the request to the json-server and get the response. The received response is stored in the response object.

Here the request is made for postid =1

5.4 Creating Request for POST method:

Here we are using the POST method to add the information to the /profile route:

postid = 3 and name = raju

5.5 Deserialization

RestSharp contains inbuilt de-serializers that support XML and JSON. The correct de-serializer is chosen by RestSharp, based on the content type returned by the server.

Deserialize method converts the string form of json to object data. After that, we add data to the dictionary list.

5.6 Verifying Response

Assert class is used to verify various assertions. Here we are verifying the “author” name for the corresponding postid i.e. 1. RestSharp provides the capability to assert various data items in the response.

6. Build UnitTest

Again build the UnitTest1.cs file by the following command

the result will be as shown in the figure:

7. Configuration of vscode with .Net Test Explorer

You need to config the vscode with .net test explorer to execute UnitTest. For this go to vscode settings(you can find it from the bottom left corner) and click on it.

Follow the following instructions for configuration

Reopen vscode and you can see the test cases like this.

8. Executing the Test cases

Now run the test cases by clicking the arrow button shown in the figure from step 7.

Ohhh!!! There is an error,

We forgot to run json-server.

So make sure that you run your json-server from the same restsharpSpecFlow folder by using the command:

The new terminal window of opened json-server will look like this

Now again run the test cases(as illustrated in step 8).

You can verify that our test cases executed properly by a green tick mark and if it fails, it will be shown by a red cross(X) mark.

(B) SpecFlow Integration

  1. Create specflow.json file:

To create a specflow.json file using the following instructions.

Or, If you do not see any .vscode folder then you can create a specflow.json file inside your project folder.

The use of this file is that it will help SpecFlow to understand the language of the instructions specified in the Feature file.

Paste this code into the specflow.json file and save it.

2. Creating folders:

Right-click on the sidebar and create 2 folders inside the project:

I. Feature,

II. Steps

Open Feature folder. Right-click on the Feature folder and Create a file and name it as GetPost.feature

Open Steps folder. Right-click on the Steps folder and Create a file and name it as GetPost.steps.cs

now reopen your GetPost.feature file and insert the following scenario.

Here, we are specifying the scenario

Given: Our specified pre-condition is like this wants to perform GET operation with respect to postid.

And: Specifically for postid = 1

Then: We want to verify that the “author ”name should be “typicode ”for the received response of postid = 1

Now open GetPost.Steps.cs file and paste the following code

The GetPost.Steps.cs file provides the connection between the feature file and the application interface. In the feature file, we have specified instructions and here all the instructions are implemented. For example,

Now build your project again by using the command.

When you successfully build your project you can see in test explorer, that there is new test case is added which called Feature.GetPostFeature.

Now run all test cases by pressing the run all test button(triangular play button).

Final result:

Well, you know how to Test rest API by using RestSharp and SpecFlow on the dotnet environment.

For more information on

  • The json-server is a popular tool for front-end developers to quickly setting up a fully fake REST API.
  • NUnit is a unit-testing framework for .NET applications in which the entire application is divided into modules and each module is tested independently. This Framework provides a number of attributes like Test-Fixtures, Test methods, ExpectedException, and Ignore methods.
  • NuGet Package manager is a CLI for installing .Net core packages.
  • This .NET Core framework runs on different operating systems like Windows, macOS, and Linux.
  • RestSharp
  • SpecFlow
  • Visual Studio Code
  • Code Repo

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