Quick Start on Testing

The Ballerina Language has a built-in robust test framework, which allows you to achieve multiple levels of the test pyramid including unit testing, integration testing, and end to end testing. It provides features such as assertions, data providers, mocking, and code coverage, which enable the programmers to write comprehensive tests.

Writing a Simple Function

To get started, let’s write a simple Ballerina function and test it.

  1. First, let’s create a Ballerina package. Use the bal new command to create the package. For more information on the command, see Structuring Ballerina Code.

    A tests directory needs to be created to store the test files. In this example, the main_test.bal test file needs to be added within a tests directory.

  2. Let’s write a function which handles sending a get request in the main.bal file of the default module.

     // main.bal
     import ballerina/io;
     import ballerina/http;
     import ballerina/regex;
     http:Client clientEndpoint = check new ("https://api.chucknorris.io/jokes/");
     // This function performs a `get` request to the Chuck Norris API and returns a random joke 
     // with the name replaced by the provided name or an error if the API invocation fails.
     function getRandomJoke(string name) returns @tainted string|error {
         http:Response response = check clientEndpoint->get("/random");
         if (response.statusCode == http:STATUS_OK) {
             var payload = response.getJsonPayload();
             if (payload is json) {
                 json joke = check payload.value;
                 string replacedText = regex:replaceAll(joke.toString(), "Chuck Norris", name);
                 return replacedText;
         } else {
             error err = error("error occurred while sending GET request");
             io:println(err.message(), ", status code: ", response.statusCode, ", reason: ", response.getJsonPayload());
             return err;
         error err = error("error occurred while sending GET request");
         return err;
  3. Now, let’s write a simple test case to verify the behavior of the main function in the main_test.bal file.

     // main_test.bal
     import ballerina/io;
     import ballerina/test;
     import ballerina/http;
     // This test function tests the behavior of the `getRandomJoke` when
     // the API returns a successful response.
     @test:Config {}
     function testGetRandomJoke() {
         // Create a default mock HTTP Client and assign it to the `clientEndpoint`
         clientEndpoint = test:mock(http:Client);
         // Stub the behavior of the `get` function to return the specified mock response.
         // Invoke the function to test.
         string result = checkpanic getRandomJoke("Sheldon");
         // Verify the return value.   
         test:assertEquals(result, "When Sheldon wants an egg, he cracks open a chicken.");
     // Returns a mock HTTP response to be used for the jokes API invocation.
     function getMockResponse() returns http:Response {
         http:Response mockResponse = new;
         json mockPayload = {"value":"When Chuck Norris wants an egg, he cracks open a chicken."};
         return mockResponse;
  4. Finally, let’s execute the tests using the following command.

    $ bal test --code-coverage

    This will print an output similar to the following.

     Compiling source
     Running Tests with Coverage
     When Sheldon wants an egg, he cracks open a chicken.
         [pass] testGetRandomJoke
         1 passing
         0 failing
         0 skipped
     Generating Test Report

What’s Next?

Now, that you have an understanding of how a test case can be written and executed, you can dive deep into the available features in the Writing Tests section.