Zenth has a built-in test runner that discovers and runs test functions. Test files live in a tests/ directory and use the _test.zn suffix.

#Writing Tests

Create a file ending with _test.zn in a tests/ directory. Define test functions that start with test_:

// tests/math_test.zn

fn test_addition() {
    AssertEq(2 + 3, 5);
}

fn test_negative_numbers() {
    AssertEq(-3 + 3, 0);
    Assert(-1 < 0);
}

Test files do not need a fn main() – the test runner generates one automatically.

#Assertions

Two assertion functions are available in all Zenth programs, not just test files:

#Assert(condition)

Panics if condition is false, reporting the file and line number:

Assert(Len("hello") == 5);
Assert(x > 0);
Assert(items.exists("key"));

On failure:

assert failed at tests/math_test.zn:4

#AssertEq(got, expected)

Panics if got != expected, reporting the file, line, and both values:

AssertEq(add(2, 3), 5);
AssertEq(name.upper(), "ALICE");
AssertEq(Len(items), 3);

On failure:

assert_eq failed at tests/math_test.zn:8
  expected: 5
       got: 4

AssertEq uses the == operator, so both values must be the same comparable type.

#Running Tests

Run all tests in the default tests/ directory:

zenth test

Run tests in a specific directory:

zenth test path/to/tests/

Run a single test file:

zenth test tests/math_test.zn

#Output Format

The test runner prints results in plain text:

tests/math_test.zn
  test_addition ... PASS
  test_negative_numbers ... PASS
tests/strings_test.zn
  test_upper ... PASS
  test_split ... FAIL
    assert_eq failed at tests/strings_test.zn:12
      expected: 3
           got: 2

3 passed, 1 failed

The exit code is 0 if all tests pass, 1 if any test fails.

#Testing with Module Imports

Test files can import local modules just like regular programs. Use ../ to navigate from the tests/ directory to your source modules:

project/
  src/
    task.zn          ← module with Task obj and parse_task fn
  tests/
    task_test.zn     ← imports ../src/task

// src/task.zn
obj Task {
    name: Str;
    state: Str;
}

fn parse_task(line: Str) -> Task {
    return Task(name=line, state="todo");
}

// tests/task_test.zn
import "../src/task";

fn test_parse_task() {
    let t = task.parse_task("buy milk");
    AssertEq(t.name, "buy milk");
    AssertEq(t.state, "todo");
}

fn test_construct_task() {
    let t = task.Task(name="clean", state="done");
    AssertEq(t.name, "clean");
    AssertEq(t.state, "done");
}

Module imports in test files support all the same features as in regular programs: function calls, object constructors with named arguments, method calls, and qualified type annotations like Array(task.Task).

Important: Import paths must start with ./ or ../ to be recognized as local modules. Writing import "src/task" without the prefix will produce an error.

#Conventions

• Test files: *_test.zn in a tests/ directory
• Test functions: fn test_*() with no parameters and no return type
• One tests/ directory at the project root is the default location
• Use Assert for boolean conditions, AssertEq for value comparison
• Helper functions (without the test_ prefix) can be defined in test files and called from test functions

#Example: Testing an Object

// tests/rectangle_test.zn

obj Rectangle {
    width: Float;
    height: Float;

    fn area() -> Float {
        return self.width * self.height;
    }
}

fn test_area() {
    let r = Rectangle(width=3.0, height=4.0);
    AssertEq(r.area(), 12.0);
}

fn test_zero_area() {
    let r = Rectangle(width=0.0, height=100.0);
    AssertEq(r.area(), 0.0);
}

#Example: Testing with Collections

// tests/collections_test.zn

fn test_array_operations() {
    let nums = [3, 1, 4, 1, 5];
    AssertEq(nums.max(), 5);
    AssertEq(nums.min(), 1);
    AssertEq(nums.sum(), 14);

    let sorted = nums.sorted();
    AssertEq(sorted[0], 1);
    AssertEq(sorted[4], 5);
}

fn test_hashmap_lookup() {
    var scores = Hashmap(Str,Int);
    scores["alice"] = 95;
    scores["bob"] = 80;

    Assert(scores.exists("alice"));
    AssertEq(scores["alice"], 95);
    AssertEq(Len(scores), 2);
}