JUnit Assumptions assumeTrue Method

The assumeTrue method in JUnit is used to conditionally skip a test based on a given assumption. If the assumption evaluates to false, the test is aborted. JUnit provides several overloaded versions of this method to handle different scenarios and to provide custom messages for test aborts. This guide covers the basics of using the assumeTrue method, including its syntax and examples of its different overloads.

Table of Contents

1. Introduction
2. assumeTrue Method Syntax
3. Examples
   • Basic Usage
   • Using a Custom Message
   • Using a Message Supplier
   • Using a Boolean Supplier
4. Real-World Use Case
5. Conclusion

Introduction

The assumeTrue method in JUnit’s Assumptions class allows you to conditionally skip tests if a given assumption evaluates to false. This is useful for scenarios where certain preconditions are required for the test to proceed, and it makes sense to skip the test rather than fail it if those conditions are not met.

assumeTrue Method Syntax

Here is the basic syntax of the assumeTrue method with its different overloads:

// Validates the given assumption and aborts the test if it evaluates to false
static void assumeTrue(boolean assumption);

// Validates the given assumption and aborts the test if it evaluates to false, with a custom message
static void assumeTrue(boolean assumption, String message);

// Validates the given assumption and aborts the test if it evaluates to false, with a custom message supplier
static void assumeTrue(boolean assumption, Supplier<String> messageSupplier);

// Validates the given assumption and aborts the test if it evaluates to false, using a BooleanSupplier
static void assumeTrue(BooleanSupplier assumptionSupplier);

// Validates the given assumption and aborts the test if it evaluates to false, using a BooleanSupplier with a custom message
static void assumeTrue(BooleanSupplier assumptionSupplier, String message);

// Validates the given assumption and aborts the test if it evaluates to false, using a BooleanSupplier with a custom message supplier
static void assumeTrue(BooleanSupplier assumptionSupplier, Supplier<String> messageSupplier);

Parameters:

• assumption: The boolean assumption to be validated.
• assumptionSupplier: A supplier that provides the boolean assumption to be validated.
• message: Optional. A custom message to display if the assumption evaluates to false.
• messageSupplier: Optional. A supplier that provides a custom message to display if the assumption evaluates to false.

Returns:

• Nothing. The method always throws an org.opentest4j.TestAbortedException if the assumption evaluates to false.

Examples

Basic Usage

Validate an assumption and abort the test if it evaluates to false.

Example

import static org.junit.jupiter.api.Assumptions.assumeTrue;
import org.junit.jupiter.api.Test;

public class AssumeTrueTest {
    @Test
    void testAssumeTrue() {
        assumeTrue(true);
    }
}

Using a Custom Message

Validate an assumption and abort the test if it evaluates to false, with a custom message.

Example

import static org.junit.jupiter.api.Assumptions.assumeTrue;
import org.junit.jupiter.api.Test;

public class CustomMessageTest {
    @Test
    void testAssumeTrueWithMessage() {
        assumeTrue(true, "The assumption evaluated to true, test proceeds");
    }
}

Using a Message Supplier

Validate an assumption and abort the test if it evaluates to false, with a message retrieved from a message supplier.

Example

import static org.junit.jupiter.api.Assumptions.assumeTrue;
import org.junit.jupiter.api.Test;
import java.util.function.Supplier;

public class MessageSupplierTest {
    @Test
    void testAssumeTrueWithMessageSupplier() {
        Supplier<String> messageSupplier = () -> "The assumption evaluated to true, test proceeds";
        assumeTrue(true, messageSupplier);
    }
}

Using a Boolean Supplier

Validate an assumption using a BooleanSupplier and abort the test if it evaluates to false.

Example

import static org.junit.jupiter.api.Assumptions.assumeTrue;
import org.junit.jupiter.api.Test;
import java.util.function.BooleanSupplier;

public class BooleanSupplierTest {
    @Test
    void testAssumeTrueWithBooleanSupplier() {
        BooleanSupplier assumptionSupplier = () -> true;
        assumeTrue(assumptionSupplier);
    }
}

Using a Boolean Supplier with a Custom Message

Validate an assumption using a BooleanSupplier and abort the test if it evaluates to false, with a custom message.

Example

import static org.junit.jupiter.api.Assumptions.assumeTrue;
import org.junit.jupiter.api.Test;
import java.util.function.BooleanSupplier;

public class BooleanSupplierWithMessageTest {
    @Test
    void testAssumeTrueWithBooleanSupplierAndMessage() {
        BooleanSupplier assumptionSupplier = () -> true;
        assumeTrue(assumptionSupplier, "The assumption evaluated to true, test proceeds");
    }
}

Using a Boolean Supplier with a Message Supplier

Validate an assumption using a BooleanSupplier and abort the test if it evaluates to false, with a message retrieved from a message supplier.

Example

import static org.junit.jupiter.api.Assumptions.assumeTrue;
import org.junit.jupiter.api.Test;
import java.util.function.BooleanSupplier;
import java.util.function.Supplier;

public class BooleanSupplierWithMessageSupplierTest {
    @Test
    void testAssumeTrueWithBooleanSupplierAndMessageSupplier() {
        BooleanSupplier assumptionSupplier = () -> true;
        Supplier<String> messageSupplier = () -> "The assumption evaluated to true, test proceeds";
        assumeTrue(assumptionSupplier, messageSupplier);
    }
}

Real-World Use Case

Testing a Feature that Requires a Specific Environment

A common use case for assumeTrue is testing features that require a specific environment or configuration. For example, skipping a test if a certain system property is not set.

Example

import static org.junit.jupiter.api.Assumptions.assumeTrue;
import org.junit.jupiter.api.Test;

public class EnvironmentTest {
    @Test
    void testFeatureInSpecificEnvironment() {
        String env = System.getProperty("env");
        assumeTrue("development".equals(env), "Test only runs in development environment");
        // Test logic for development environment
    }
}

In this example, the EnvironmentTest class uses assumeTrue to skip a test if the env system property is not set to "development". This ensures that the test only runs in the development environment.

Conclusion

The assumeTrue method in JUnit’s Assumptions class is used for conditionally skipping tests based on assumptions. By using assumeTrue and its various overloads, you can ensure that your tests are skipped when preconditions or assumptions are not met, providing clear feedback when tests are not executed. Understanding and using the assumeTrue method effectively is crucial for developing robust and maintainable Java applications.