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This guide covers how to write, run, and debug tests in the OpenRocket codebase.

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Unit testing

OpenRocket uses JUnit 5 (Jupiter) as its testing framework. Tests are organized in separate source trees from production code:
  • core/src/test/java — tests for core functionality
  • swing/src/test/java — tests for Swing UI components

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Running tests

# Run all tests
./gradlew test

# Run tests for a specific module
./gradlew core:test
./gradlew swing:test

# Run a specific test class
./gradlew core:test --tests "info.openrocket.core.util.MathUtilTest"

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Test structure

Tests in OpenRocket follow standard JUnit 5 conventions:
  • Test class names end with Test (for example, MathUtilTest)
  • Test methods are annotated with @Test
  • Many tests extend BaseTestCase, which provides common setup and utilities

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Example test

package info.openrocket.core.util;

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.*;

public class ExampleTest extends BaseTestCase {

    @Test
    public void testSomeFeature() {
        // Arrange
        SomeClass instance = new SomeClass();

        // Act
        int result = instance.someMethod();

        // Assert
        assertEquals(42, result);
    }
}

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Writing good tests

1

Test one thing per method

Each test method should verify a single behavior. This makes failures easy to diagnose and keeps test names meaningful.
2

Use descriptive names

Name test methods so that the failure message explains exactly what is broken — for example, testNoseConeVolumeWithZeroLength.
3

Follow Arrange-Act-Assert

Structure your test body in three sections: set up the state, execute the code under test, then assert the outcome.
4

Mock external dependencies

Isolate the unit under test by mocking databases, file system access, or other external services.
5

Test edge cases and error conditions

Cover boundary values, null inputs, and exception paths — not just the happy path.
6

Keep tests independent

Tests must not share mutable state. Each test should be able to run in any order and produce the same result.

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Code coverage

OpenRocket uses JaCoCo to track and enforce test coverage. Coverage verification runs automatically during JAR packaging.
ModuleCoverage threshold
core60% minimum
swingDisabled (0%) — limited test coverage
If the core module falls below the 60% coverage threshold, JAR packaging will fail. Fix failing or missing tests before merging.

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Generating coverage reports

# Generate an aggregate coverage report
./gradlew test jacocoRootReport

# Run the full build (includes coverage verification)
./gradlew build
After running, HTML reports are available at:
  • build/reports/jacoco/ — aggregate report
  • core/build/reports/jacoco/ — core module report
  • swing/build/reports/jacoco/ — Swing module report
A GitHub Actions workflow publishes coverage reports automatically on every push to the main branch, making it easy to track coverage trends over time.

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Debugging

The most effective debugging tool is your IDE’s built-in debugger. Both IntelliJ IDEA and Eclipse offer full Java debugging support.
1

Set breakpoints

Click in the gutter next to the line you want to pause on. Conditional breakpoints let you pause only when a specific expression evaluates to true — useful in tight loops.
2

Run in debug mode

In IntelliJ IDEA, use the debug run configuration (the bug icon) instead of the normal run. In Eclipse, choose Run > Debug As > Java Application.
3

Inspect variables and call stack

When execution pauses at a breakpoint, inspect local variables in the Variables panel and navigate the call stack in the Debug panel. Use Evaluate Expression to run arbitrary code at the breakpoint.

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Useful command-line debug flags

Several JVM system properties help during debugging. See Command line arguments for the full list. The most useful ones are: 
# Enable extra debug tools in the UI
java -Dopenrocket.debug -jar OpenRocket.jar

# Show the debug file menu
java -Dopenrocket.debug.fileMenu -jar OpenRocket.jar

# Enable additional runtime safety checks
java -Dopenrocket.debug.safetycheck -jar OpenRocket.jar

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