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# Backend Tools Directory
## Test Kernel
The **Test Kernel** is a drop-in replacement for Puter's main kernel. Instead of
actually initializing and running services, it only registers them and then invokes
a test iterator through all the services.
The Test Kernel is ideal for running unit and integration tests against individual services, ensuring they behave correctly.
### Usage
```
node src/backend/tools/test`
```
### Testing Services
Implement the method `_test` on any service. When `_test` is called the "construct"
phase has already completed (meaning `_construct` on your service has been called
by now if you've implemented it), but the "init" phase will never happen (so _init
is never called).
> **TODO:** I want to add support for mocking `_init` for deeper testing.
For example, it should look similar to this snippet:
```javascript
class ExampleService extends BaseService {
// ...
async _test ({ assert }) {
assert.equal('actual', 'expected', 'rule should have a description');
}
}
```
Notice the parameter `assert` - this holds the TestKernel's testing API. The
reason this is a named parameter is to leave room for future support of
multiple testing APIs if this is ever desired or we decide to migrate
incrementally.
The last parameter to `assert.equal` is a message describing the test rule.
The message should always be a short statement with minimal punctuation.
#### TestKernel's testing API
The `assert` value here is a function that also has other methods defined
in its properties. When called directly, `assert` will run the callback you
provide as an assertion. When no `name` parameter is specified, the callback
itself will be printed as the name of the assertion - this is useful for
very short expressions which are self-descriptive.
```javascript
class ExampleService extends BaseService {
// ...
async _test ({ assert }) {
assert(() => 1 === 2, 'one should equal two');
assert.equal(1, 2, 'one should equal two')
assert(() => 3 === 4); // prints out as: `() => 3 === 4`
}
}
```
| Method | Parameters | Types | Description |
|----------------|---------------------------------|---------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------|
| `assert` | `callback`, `name?` | `callback: () => boolean`, `name?: string` | Runs the callback as an assertion. If `name` is omitted, the callback's source text is used as the printed name of the assertion. |
| `assert.equal` | `actual`, `expected`, `message` | `actual: any`, `expected: any`, `message: string` | Asserts that `actual === expected`. The final parameter is a short descriptive message for the test rule. |
### Test Kernel Notes
1. **Logging**:
A custom `TestLogger` is provided for simplified logging output during tests.
Since LogService is never initialized, this is never replaced.
2. **Context Management**:
The Test Kernel uses the same `Context` system as the main Kernel. This gives test environments a consistent way to access global state, configuration, and service containers.
3. **Assertion & Results Tracking**:
The Test Kernel includes a simple testing structure that:
- Tracks passed and failed assertions.
- Repeats assertion outputs at the end of test runs for clarity.
- Allows specifying which services to test via command-line arguments.
### Typical Workflow
1. **Initialization**:
Instantiate the Test Kernel, and add any modules you want to test.
2. **Module Installation**:
The Test Kernel installs these modules (via `_install_modules()`), making their services available in the `Container`.
3. **Service Testing**:
After modules are installed, each service can be constructed and tested. Tests are implemented as `_test()` methods on services, using simple assertion helpers (`testapi.assert` and `testapi.assert.equal`).
4. **Result Summarization**:
Once all tests run, the Test Kernel prints a summary of passed and failed assertions, aiding quick evaluation of test outcomes.
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