How to Run a Single JUnit Test from the Command Line Without Modifying Source Code

How can I execute a specific test method from a JUnit test class using the command line without modifying the source code?

Running a specific test method from a JUnit test class directly from the command line can be efficiently achieved using the JUnit Console Runner in a simple manner. This allows developers to focus testing efforts on particular scenarios without the need for changing the source code or integrating complex project dependencies like Maven.

# Example command to run a specific JUnit test method
java -cp path/to/junit-platform-console-standalone-1.8.0.jar org.junit.platform.console.ConsoleLauncher --select-test org.package.ClassName.testMethodName

Causes

• The default command line execution requires specifying the full test class but does not directly support running individual test methods.
• JUnit versions before 5 do not offer direct support to run test methods without some form of bridge or tool.

Solutions

• Utilize the JUnit 5 command-line launcher instead of JUnit 4, as it supports running specific test methods without modifying the test class.
• The command format is as follows: `java -jar junit-platform-console-standalone-1.x.x.jar --select-test <fully.qualified.classname.methodname>`.
• For instance: `java -jar junit-platform-console-standalone-1.8.0.jar --select-test org.package.ClassName.testMethodName`.
• Ensure the JUnit platform console jar is included in your classpath to avoid dependency issues without using Maven.

Mistake: Not including the correct JUnit Platform console jar in the classpath.

Solution: Ensure that the complete path to the JUnit Platform Console Launcher jar file is provided.

Mistake: Mentioning class or method names incorrectly (typos or case sensitivity issues).

Solution: Verify the fully qualified names for both the class and method, ensuring proper casing.

Mistake: Using an incompatible version of JUnit.

Solution: Make sure to use JUnit 5 or later for this method to work.