TestLang++: HTTP API Testing DSL

A domain-specific language for writing HTTP API tests that compiles to JUnit 5 test cases.

What it does

TestLang++ lets you write API tests in a simple, readable syntax instead of verbose Java code. You define your tests in .test files, and the compiler generates executable JUnit 5 tests that use Java's HttpClient.

How it works

The compiler uses JFlex for lexical analysis and CUP for parsing. It builds an abstract syntax tree (AST) from your .test file, then generates JUnit 5 code.

.test file → JFlex → CUP → AST → Code Generator → GeneratedTests.java

Project structure

├── src/
│   ├── ast/              # AST classes
│   ├── TestLang.flex     # Lexer rules
│   ├── TestLang.cup      # Parser grammar
│   ├── CodeGenerator.java
│   └── Main.java
├── examples/             # Sample .test files
├── lib/                  # JFlex, CUP, JUnit jars
├── backend/              # Test server
└── GeneratedTests.java   # Output

Syntax

Configuration

config {
    base_url = "http://localhost:8080";
    header "Content-Type" = "application/json";
}

Variables

let user = "admin";
let id = 42;

Tests

test Login {
    POST "/api/login" {
        body = "{ \"username\": \"$user\", \"password\": \"1234\" }";
    };
    expect status = 200;
    expect header "Content-Type" contains "json";
    expect body contains "\"token\":";
}

Supported operations

• HTTP methods: GET, POST, PUT, DELETE
• Assertions: expect status = 200, expect header "key" contains "value", expect body contains "text"

Getting started

You'll need Java 8+ and three terminal windows.

Terminal 1: Build the compiler

chmod +x build-all.sh
./build-all.sh

Terminal 2: Start the test server

cd backend
mvn spring-boot:run

Terminal 3: Run the tests

java -jar lib/junit-platform-console-standalone-1.9.3.jar --class-path . --scan-class-path

Manual build (to see each step)

# Generate lexer and parser
java -jar lib/jflex-full-1.9.1.jar src/TestLang.flex
java -jar lib/java-cup-11b.jar -destdir src -parser TestLangParser -symbols sym src/TestLang.cup

# Compile everything
javac -cp "lib/java-cup-11b-runtime.jar:src" -d build src/ast/*.java
javac -cp "lib/java-cup-11b-runtime.jar:src" -d build src/CodeGenerator.java
javac -cp "lib/java-cup-11b-runtime.jar:src" -d build src/TestLangScanner.java src/TestLangParser.java src/sym.java
javac -cp "lib/java-cup-11b-runtime.jar:build" -d build src/Main.java

# Run compiler on a test file (defaults to example.test)
java -cp "lib/java-cup-11b-runtime.jar:build" Main examples/example.test
# Or run the second example:
java -cp "lib/java-cup-11b-runtime.jar:build" Main examples/example2.test

# Compile and run generated tests
javac -cp "lib/junit-platform-console-standalone-1.9.3.jar:." GeneratedTests.java
java -jar lib/junit-platform-console-standalone-1.9.3.jar --class-path . --scan-class-path

Example

Here's what a .test file looks like:

config {
    base_url = "http://localhost:8080";
    header "Content-Type" = "application/json";
}

let user = "admin";
let id = 42;

test Login {
    POST "/api/login" {
        body = "{ \"username\": \"$user\", \"password\": \"1234\" }";
    };
    expect status = 200;
    expect header "Content-Type" contains "json";
    expect body contains "\"token\":";
}

test GetUser {
    GET "/api/users/$id";
    expect status = 200;
    expect body contains "\"id\":42";
}

The compiler generates JUnit 5 tests that use Java's HttpClient to make the actual HTTP requests and verify the responses.

Dependencies

• JFlex 1.9.1 (lexer generator)
• CUP 11b (parser generator)
• JUnit 5 (testing framework)
• Java HttpClient (HTTP client)