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Giorgio Fraccavento
Giorgio Fraccavento

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

#java #testing #opensource #unittest

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);
}
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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
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2. Multiple Usage Modes

CLI:

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

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

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

Why This Matters

Test code is essential but tedious. Most developers:

  1. Copy-paste from existing tests
  2. Manually set up boilerplate
  3. Fill in placeholder assertions
  4. Run tests to see what breaks

With Test Generator:

  1. One command
  2. Complete test skeleton
  3. Ready to customize
  4. 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
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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
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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");
    }
}
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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!

Links

Have you used a tool like this before? What features would you want to see?

Let me know in the comments! 👇

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