There are many free and open-source testing tools available to help with software testing. Some of the most popular include:

Selenium: Selenium is an open-source library for automating web browsers. It supports multiple programming languages and is used for web application testing.

WebDriver driver = new ChromeDriver();
driver.get("https://www.example.com");

Appium: Appium is a similar automation framework for testing native and hybrid mobile apps. It uses the same API as Selenium.

AndroidDriver driver = new AndroidDriver<>(new URL("http://localhost:4723/wd/hub"), capabilities);

JMeter: JMeter is an open-source load testing tool used to measure the performance of web applications under heavy load.

SoapUI: SoapUI is used for testing web services and APIs. It can test SOAP and REST endpoints.

Robot Framework: Robot Framework is a generic test automation framework for acceptance testing and robotic process automation. It uses Python or Java.

*** Test Cases ***

Test Login
Open Browser URL

Input Text username testuser

Input Password password testpass
Click Button Login

Watir: Watir is a Ruby library for automating web browsers. It works with Chrome, Firefox, Edge, Safari and Internet Explorer.

browser = Watir::Browser.new :chrome
browser.goto 'http://www.google.com'

JUnit: JUnit is a unit testing framework for Java. It is used to write and run repeatable tests.

Robotium: Robotium is an Android test automation framework that extends JUnit and allows you to control Android applications.

In summary, there are many free open-source testing tools available to choose from depending on your needs and programming language preferences. The above list covers some of the most popular options for web, API, load, mobile and unit testing.