test-quality

Test Quality Skill (JUnit 5 + AssertJ)

Write high-quality, maintainable tests for Java projects using modern best practices.

When to Use

• Writing new test classes
• Reviewing/improving existing tests
• User asks to "add tests" / "improve test coverage"
• Code review mentions missing tests

Framework Preferences

JUnit 5 (Jupiter)

import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Nested;
import static org.assertj.core.api.Assertions.*;

AssertJ over standard assertions

✅ Use AssertJ:

assertThat(plugin.getState())
    .as("Plugin should be started after initialization")
    .isEqualTo(PluginState.STARTED);

assertThat(plugins)
    .hasSize(3)
    .extracting(Plugin::getId)
    .containsExactly("plugin1", "plugin2", "plugin3");

❌ Avoid JUnit assertions:

assertEquals(PluginState.STARTED, plugin.getState()); // Less readable
assertTrue(plugins.size() == 3); // Less descriptive failures

Test Structure (AAA Pattern)

Always use Arrange-Act-Assert pattern:

@Test
@DisplayName("Should load plugin from valid directory")
void shouldLoadPluginFromValidDirectory() {
    // Arrange - Setup test data and dependencies
    Path pluginDir = Paths.get("test-plugins/valid-plugin");
    PluginLoader loader = new DefaultPluginLoader();
    
    // Act - Execute the behavior being tested
    Plugin plugin = loader.load(pluginDir);
    
    // Assert - Verify results
    assertThat(plugin)
        .isNotNull()
        .extracting(Plugin::getId, Plugin::getVersion)
        .containsExactly("test-plugin", "1.0.0");
}

Naming Conventions

Test class names

// Class under test: PluginManager
PluginManagerTest           // ✅ Simple, standard
PluginManagerShould         // ✅ BDD style (if team prefers)
TestPluginManager           // ❌ Avoid

Test method names

Option 1: should_expectedBehavior_when_condition (descriptive)

@Test
void should_throwException_when_pluginDirectoryNotFound() { }

@Test  
void should_returnEmptyList_when_noPluginsAvailable() { }

@Test
void should_loadPluginsInDependencyOrder_when_multipleDependencies() { }