Unit tests focus on individual pieces of code while integration tests assess how different components interact with each other; smoke tests detect major issues before moving onto further depth testing; and regression tests make sure no changes have broken existing functionality within your applications' codebase.  Unit Test   A Unit Test is a type of software testing that focuses on individual units or components of code and verifies their correctness. The purpose of a unit test is to validate that each unit of the software performs as designed. This type of test isolates a section of code and determines if its output is correct under certain conditions. These tests are usually conducted using automated tools like JUnit, NUnit, and Jasmine.   Integration Test   Integration Tests are used to verify the functionality between different units or components within the system being tested. They are designed to evaluate how well different parts of an application work together as a whole. Unlike Unit Tests which focus on individual components, Integration Tests focus on multiple components interacting with each other in order to verify that all elements are working properly together. These tests can be performed manually or through automation tools like Selenium WebDriver and Cucumber.   Smoke Test   A Smoke Test is a type of testing used to identify any major problems with an application before performing further in-depth testing. It is often referred to as "Build Verification Testing" because its primary purpose is to determine if a build (stable version) is ready for further testing or not. This type of testing involves running basic functional tests against the application in order to ensure that its most critical functions are working correctly before moving forward with more detailed testing procedures such as regression tests and integration tests.   Regression Test   Regression Testing is used to verify that changes made have not broken existing functionality in an application's codebase. It helps ensure that new updates have not caused any unwanted side effects in areas where they were not intended or expected. Regression Tests can be either manual or automated depending on the complexity and size of the project being tested, but they are typically done using some sort of automation tool such as Selenium WebDriver or Robot Framework Suite.