Testing Morph Apps

How we test Morph itself, and how you can test apps built with it.

Testing the Translator (Fixture Suite)

The JS/TS → C++ translator is covered by fixture tests in tests/translate/:

# Full suite (translates each .ts, compiles with g++-14, runs, diffs vs Node)
python3 -m pytest tests/translate -v

How each fixture works (tests/translate/test_rust_translate.py):

1. morph <fixture>.ts --to cpp generates <fixture>.cpp
2. Test patches "../../runtime/cpp/..." includes to absolute paths
3. Compiles: g++-14 -std=c++23 <gen>.cpp runtime/cpp/net/net.cpp runtime/cpp/reactivity/task.cpp -I runtime/cpp
4. Runs the binary (must exit 0)
5. Compares stdout line-by-line against npx tsx <fixture>.ts (numeric tolerance, case-insensitive bools)

Fixtures (tests/translate/fixtures/):

Fixture	Covers
01_variables	let/const/var, primitives, inference
02_functions	functions, arrows, defaults, recursion, generics
03_classes	classes, ctors, this, static, new
04_arrays	literals, .length, index, push, spread, nesting
05_objects	literals, shorthand, computed, nesting
06_control_flow	if/switch/for/while/do-while, break/continue
07_operators	arithmetic, comparison, ===/!==, ??, +=
08_template_literals	`Hi ${x}`, nesting, expressions
09_try_catch	throw, try/catch/finally, nesting
10_console_log	multi-type/multi-arg console.log
11_complex	classes + arrays + templates together
12_string_methods	length, toUpperCase, split, slice, ...
13_number_methods	arithmetic, toString(), templates
14_inheritance	extends, super, interfaces, enums
15_chaining	s.split().length, method chains
16_loops	loop variants, break/continue, while(true)
17_async	async/await, fetch, async arrows/methods
18_promises	Promise<T>, new Promise, Promise<void>, generics
19_fetch	top-level await fetch, loops, dynamic URLs
20_cpp_types	int/int32/uint/float/char/size_t, std::vector, std::optional

Extra regression checks:

• JsNumber + println uses <print> but no explicit <format>
• Template vars (`a${x},b${y}`) require <format> + std::format
• Plain vars require neither <format> nor <print> extras

Testing the Compiler Crates

# All Rust unit tests
cargo test --workspace

# Single crate
cargo test -p morph-ir
cargo test -p morpher
cargo test -p morph-parser

Testing Your App

1. Lint First (Fastest Feedback)

morph check
morph check src/App.mx

Catches unsupported elements, props, events, CSS, and JS before compiling.

2. Dev Mode Smoke Test

morph dev

• Window opens, edits hot-reload
• Press F12 → Logs tab shows console.log output
• Network tab shows fetch() traffic

3. Logic Unit Tests (Recommended Pattern)

Keep pure logic in functions that don't touch JSX, then test the generated C++ directly:

// src/App.mx
export function add(a: number, b: number): number {
  return a + b;
}

morph logic.ts --to cpp   # extract logic to a file, or copy the function
g++-14 -std=c++23 -I runtime/cpp test_main.cpp runtime/cpp/net/net.cpp -o test_app
./test_app

Or test the TypeScript directly with Node before compiling:

npx tsx src/logic.ts

4. Golden-Output Tests

Same pattern the translator suite uses — compare app output vs expected:

morph build --output bin/
./bin/my-app --headless --dump-state > actual.txt
diff expected.txt actual.txt

5. CI Example

# .github/workflows/test.yml
name: Test
on: [push, pull_request]
jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: dtolnay/rust-toolchain@stable
      - run: sudo apt update && sudo apt install -y g++-14 cmake libglfw3-dev libfreetype-dev libharfbuzz-dev
      - run: cargo test --workspace
      - run: python3 -m pytest tests/translate -x -q
      - run: cargo install --path crates/morphc
      - run: morph check
      - run: morph build

Debugging Failing Tests

Symptom	What To Check
Fixture output differs by whitespace	Tests compare line-by-line; check trailing spaces, println vs print
g++-14: command not found	Install GCC 14 (apt install g++-14) or set build.cxx
npx tsx fails	npm i -D tsx, Node 18+ required
.cpp has wrong includes	Check Ctx::need() / headers_for() in type_resolver.rs
Async test hangs	Missing process_tasks() loop, un-awaited Result

Writing New Fixture Tests

1. Add tests/translate/fixtures/21_my_feature.ts (must run clean under npx tsx)
2. Run python3 -m pytest tests/translate -k 21_my_feature -v
3. Generated .cpp is gitignored (tests/translate/fixtures/*.cpp) — only commit the .ts

Related

• Debugging & Profiling — GDB, sanitizers, DevTools
• Intent-Based Codegen — how declarations, widening, and helpers are chosen
• Runtime Internals — signals, coroutines, scene graph