How to test code dependent on environment variables using JUnit?

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

import static com.github.stefanbirkner.systemlambda.SystemLambda.*;

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.

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