assumingThat for conditional assertions in JUnit

Introduction

We use assumingThat to run some checks only when certain conditions are true. This helps skip tests that don't apply in some cases.

When you want to test a feature only if a specific environment variable is set.

When you want to run a test only if the operating system is Windows.

When you want to check a value only if a user is logged in.

When you want to skip some assertions if a certain configuration is missing.

Syntax

JUnit

assumingThat(condition, executable);

condition is a boolean expression that decides if the test inside runs.

executable is the code block with assertions to run if the condition is true.

Examples

This runs the assertion only if the OS name starts with "Windows".

JUnit

assumingThat(System.getProperty("os.name").startsWith("Windows"), () -> {
    assertTrue(isWindowsFeatureEnabled());
});

This checks the user's role only if the user object is not null.

JUnit

assumingThat(user != null, () -> {
    assertEquals("admin", user.getRole());
});

Sample Program

This test checks if the OS name contains "Windows" only when the OS is Windows. On other OS, the assertion is skipped.

JUnit

import static org.junit.jupiter.api.Assumptions.assumingThat;
import static org.junit.jupiter.api.Assertions.assertTrue;
import org.junit.jupiter.api.Test;

public class ConditionalTest {

    @Test
    void testFeatureOnlyOnWindows() {
        String os = System.getProperty("os.name");
        assumingThat(os.startsWith("Windows"), () -> {
            // This assertion runs only on Windows
            assertTrue(os.contains("Windows"));
        });
    }
}

Important Notes

If the condition is false, the code inside assumingThat is skipped, not failed.

This helps avoid false failures when tests don't apply.

Summary

assumingThat runs assertions only if a condition is true.

It helps skip tests that don't apply in some situations.

Use it to make tests smarter and avoid unnecessary failures.