I Built an Open-Source Tool That Generates JUnit Tests Automatically

Giorgio Fraccavento — Mon, 13 Apr 2026 15:03:18 +0000

I Built an Open-Source Tool That Generates JUnit Tests Automatically

The Problem

As a Java developer, I noticed something frustrating: developers spend 20-30% of their time writing test boilerplate code.

Test files are typically 60-70% boilerplate:

Class declarations
Import statements
Method signatures
Placeholder assertions

This is repetitive, error-prone, and adds zero business value.

The Idea

What if I could generate a complete, runnable JUnit 5 test skeleton from a Java method in seconds?

// Input
public int somma(int a, int b) {
    return a + b;
}

// One command
./testgen.sh Calculator.java --method somma

// Output: Complete test file!
@Test
void testSomma() {
    Calculator instance = new Calculator();
    int result = instance.somma(1, 1);
    assertNotNull(result);
}

The Solution: Test Generator

I built Test Generator - an open-source tool that:

✅ Parses Java method signatures

✅ Generates complete test classes

✅ Handles all primitive types intelligently

✅ Works as CLI or library

✅ Integrates with CI/CD

Key Features

1. Intelligent Parameter Defaults

The generator automatically fills parameters with sensible defaults:

int     → 1
String  → "test"
boolean → true
double  → 1.0
float   → 1.0f
long    → 1L

2. Multiple Usage Modes

CLI:

./testgen.sh Calculator.java --method somma

Library:

StandaloneTestGenerator gen = new StandaloneTestGenerator("MyClass.java");
String test = gen.generateTestForMethod("method", "int", params, names);
gen.writeTestFile(test, "src/test/java");

3. Cross-Platform Support

Windows (.bat script)
Linux/Mac (.sh script)
GitHub Actions CI/CD included

Building It: 5-Day Timeline

I decided to build this as a rapid MVP:

Day 1: Project setup + Gradle configuration

Day 2: Method parsing + CLI interface

Day 3: Test generation engine + examples

Day 4: Documentation + refinement

Day 5: GitHub setup + v1.0.0 release

Tech Stack

Java 17+
Gradle 8.5+
JUnit 5
GitHub Actions

This stack choice was intentional:

Java 17 - modern language features
Gradle - dependency management & plugin ecosystem
JUnit 5 - modern testing framework
GitHub Actions - free CI/CD

Open Source Release

Repository: https://github.com/giofrac/test-generator

License: MIT

Release: v1.0.0 available now

The tool is production-ready and includes:

431 lines of core Java code
Complete documentation with examples
GitHub Actions CI/CD workflows
Issue templates for bug reports and features
Contribution guidelines

Real-World Impact

The Numbers

Typical developer spends 20-30% of time on test setup
Test files are 60-70% boilerplate
One method takes ~2-3 minutes to test manually
Test Generator generates in 0.5 seconds

The Value Proposition

Immediate Value - Saves time on every test file
Monetizable - Free tier + Pro features (Mockito, coverage)
Extensible - Easy to add more frameworks (TestNG, Spock)
Community-Ready - Fully documented, welcomes contributions

Why This Matters

Test code is essential but tedious. Most developers:

Copy-paste from existing tests
Manually set up boilerplate
Fill in placeholder assertions
Run tests to see what breaks

With Test Generator:

One command
Complete test skeleton
Ready to customize
Immediate productivity boost

Roadmap

Phase 1 (Complete) ✅

[x] MVP with CLI tool
[x] Java method parsing
[x] JUnit 5 generation
[x] Documentation

Phase 2 (Planned)

[ ] Full IntelliJ IDE plugin
[ ] Mockito integration
[ ] Test coverage analysis
[ ] Custom assertion templates

Phase 3 (Future)

[ ] Multiple test framework support (TestNG, Spock)
[ ] Code coverage reporting
[ ] Integration test generation
[ ] Cloud sync for test templates

Getting Started

Quick Installation

git clone https://github.com/giofrac/test-generator.git
cd test-generator
./gradlew build

Quick Start

# Generate all tests
./testgen.sh Calculator.java

# Generate for specific method
./testgen.sh Calculator.java --method somma

# Custom output directory
./testgen.sh Calculator.java --output target/test-gen

As a Library

import com.giofrac.StandaloneTestGenerator;

public class MyApp {
    public static void main(String[] args) throws IOException {
        StandaloneTestGenerator gen = new StandaloneTestGenerator("MyClass.java");

        String test = gen.generateTestForMethod(
            "myMethod",      // method name
            "String",        // return type
            new String[]{"int", "String"},   // parameter types
            new String[]{"count", "name"}    // parameter names
        );

        gen.writeTestFile(test, "src/test/java");
    }
}

The Community

I'm looking for:

✅ Java developers who want to save time
✅ Contributors interested in testing tools
✅ People who want to reduce boilerplate

This is an open-source project built to solve a real problem. Feedback and PRs welcome!

DEV Community: Giorgio Fraccavento

I Built an Open-Source Tool That Generates JUnit Tests Automatically

I Built an Open-Source Tool That Generates JUnit Tests Automatically

The Problem

The Idea

The Solution: Test Generator

Key Features

Building It: 5-Day Timeline

Tech Stack

Open Source Release

Real-World Impact

The Numbers

The Value Proposition

Why This Matters

Roadmap

Phase 1 (Complete) ✅

Phase 2 (Planned)

Phase 3 (Future)

Getting Started

Quick Installation

Quick Start

As a Library

The Community

Links