How to test code dependent on environment variables using JUnit?

Question

I have a piece of Java code which uses an environment variable and the behaviour of the code depends on the value of this variable. I would like to test this code with different values of the environment variable. How can I do this in JUnit?

I've seen some ways to set environment variables in Java in general, but I'm more interested in unit testing aspect of it, especially considering that tests shouldn't interfere with each other.

Answer 1

The library System Lambda has a method withEnvironmentVariables for setting environment variables.

public void EnvironmentVariablesTest {
  @Test
  public void setEnvironmentVariable() {
    String value = withEnvironmentVariable("name", "value")
      .execute(() -> System.getenv("name"));
    assertEquals("value", value);
  }
}

For Java 5 to 7 the library System Rules has a JUnit rule called EnvironmentVariables.

import org.junit.contrib.java.lang.system.EnvironmentVariables;

public class EnvironmentVariablesTest {
  @Rule
  public final EnvironmentVariables environmentVariables
    = new EnvironmentVariables();

  @Test
  public void setEnvironmentVariable() {
    environmentVariables.set("name", "value");
    assertEquals("value", System.getenv("name"));
  }
}

Full disclosure: I'm the author of both libraries.