What are unit tests, integration tests, smoke tests, and regression tests? What are the differences between them and which tools can I use for each of them?
For example, I use JUnit and NUnit for unit testing and integration testing. Are there any tools for the last two, smoke testing or regression testing?
Unit test: Specify and test one point of the contract of single method of a class. This should have a very narrow and well defined scope. Complex dependencies and interactions to the outside world are stubbed or mocked.
Integration test: Test the correct inter-operation of multiple subsystems. There is whole spectrum there, from testing integration between two classes, to testing integration with the production environment.
Smoke test (aka sanity check): A simple integration test where we just check that when the system under test is invoked it returns normally and does not blow up.
Regression test: A test that was written when a bug was fixed. It ensures that this specific bug will not occur again. The full name is "non-regression test". It can also be a test made prior to changing an application to make sure the application provides the same outcome.
To this, I will add:
Acceptance test: Test that a feature or use case is correctly implemented. It is similar to an integration test, but with a focus on the use case to provide rather than on the components involved.
System test: Tests a system as a black box. Dependencies on other systems are often mocked or stubbed during the test (otherwise it would be more of an integration test).
Pre-flight check: Tests that are repeated in a production-like environment, to alleviate the 'builds on my machine' syndrome. Often this is realized by doing an acceptance or smoke test in a production like environment.
Everyone will have slightly different definitions, and there are often grey areas. However:
Unit test: Verifying that particular component (i.e., class) created or modified functions as designed. This test can be manual or automated, but it does not move beyond the boundary of the component.
Integration test: Verifying that the interaction of particular components function as designed. Integration tests can be performed at the unit level or the system level. These tests can be manual or automated.
Regression test: Verifying that new defects are not introduced into existing code. These tests can be manual or automated.
Depending upon your SDLC (waterfall, RUP, agile, etc.) particular tests may be performed in 'phases' or may all be performed, more or less, at the same time. For example, unit testing may be limited to developers who then turn the code over to testers for integration and regression testing. However, another approach might have developers doing unit testing and some level of integration and regression testing (using a TDD approach along with continuous integration and automated unit and regression tests).
The tool set will depend largely on the codebase, but there are many open source tools for unit testing (JUnit). HP's (Mercury) QTP or Borland's Silk Test are both tools for automated integration and regression testing.
I just wanted to add and give some more context on why we have these levels of test, what they really mean with examples
Mike Cohn in his book “Succeeding with Agile” came up with the “Testing Pyramid” as a way to approach automated tests in projects. There are various interpretations of this model. The model explains what kind of automated tests need to be created, how fast they can give feedback on the application under test and who writes these tests. There are basically 3 levels of automated testing needed for any project and they are as follows.
Unit Tests- These test the smallest component of your software application. This could literally be one function in a code which computes a value based on some inputs. This function is part of several other functions of the hardware/software codebase that makes up the application.
For example - Let’s take a web based calculator application. The smallest components of this application that needs to be unit tested could be a function that performs addition, another that performs subtraction and so on. All these small functions put together makes up the calculator application.
Historically developer writes these tests as they are usually written in the same programming language as the software application. Unit testing frameworks such as JUnit and NUnit (for java), MSTest (for C# and .NET) and Jasmine/Mocha (for JavaScript) are used for this purpose.
The biggest advantage of unit tests are, they run really fast underneath the UI and we can get quick feedback about the application. This should comprise more than 50% of your automated tests.
API/Integration Tests- These test various components of the software system together. The components could include testing databases, API’s (Application Programming Interface), 3rd party tools and services along with the application.
For example - In our calculator example above, the web application may use a database to store values, use API’s to do some server side validations and it may use a 3rd party tool/service to publish results to the cloud to make it available across different platforms.
Historically a developer or technical QA would write these tests using various tools such as Postman, SoapUI, JMeter and other tools like Testim.
These run much faster than UI tests as they still run underneath the hood but may consume a little more time than unit tests as it has to check the communication between various independent components of the system and ensure they have seamless integration. This should comprise more that 30% of the automated tests.
UI Tests- Finally, we have tests that validate the UI of the application. These tests are usually written to test end to end flows through the application.
For example - In the calculator application, an end to end flow could be, opening up the browser-> Entering the calculator application url -> Logging in with username/password -> Opening up the calculator application -> Performing some operations on the calculator -> verifying those results from the UI -> Logging out of the application. This could be one end to end flow that would be a good candidate for UI automation.
Historically, technical QA’s or manual testers write UI tests. They use open source frameworks like Selenium or UI testing platforms like Testim to author, execute and maintain the tests. These tests give more visual feedback as you can see how the tests are running, the difference between the expected and actual results through screenshots, logs, test reports.
The biggest limitation of UI tests is, they are relatively slow compared to Unit and API level tests. So, it should comprise only 10-20% of the overall automated tests.
The next two types of tests can vary based on your project but the idea is-
Smoke Tests
This can be a combination of the above 3 levels of testing. The idea is to run it during every code check in and ensure the critical functionalities of the system are still working as expected; after the new code changes are merged. They typically need to run with 5 - 10 mins to get faster feedback on failures
Regression Tests
They usually are run once a day at least and cover various functionalities of the system. They ensure the application is still working as expected. They are more details than the smoke tests and cover more scenarios of the application including the non-critical ones.
Smoke and sanity testing are both performed after a software build to identify whether to start testing. Sanity may or may not be executed after smoke testing. They can be executed separately or at the same time - sanity being immediately after smoke.
Because sanity testing is more in-depth and takes more time, in most cases it is well worth to be automated.
Smoke testing usually takes no longer than 5-30 minutes for execution. It is more general: it checks a small number of core functionalities of the whole system, in order to verify that the stability of the software is good enough for further testing and that there are no issues, blocking the run of the planned test cases.
Sanity testing is more detailed than smoke and may take from 15 minutes up to a whole day, depending on the scale of the new build. It is a more specialized type of acceptance testing, performed after progression or re-testing. It checks the core features of certain new functionalities and/or bug fixes together with some closely related to them features, in order to verify that they are functioning as to the required operational logic, before regression testing can be executed at a larger scale.
There are some good answers already, but I would like further refine them:
Unit testing is the only form of white box testing here. The others are black box testing. White box testing means that you know the input; you know the inner workings of the mechanism and can inspect it and you know the output. With black box testing you only know what the input is and what the output should be.
So clearly unit testing is the only white box testing here.
