Testing

coretest runs an oryn application in tests, in the test environment:

• all telemetry is exported in memory, whatever the configuration,
• logs are not printed on the console,
• the logger is not set as slog.Default(), so parallel tests do not interfere.

Start the application

func TestGreet(t *testing.T) {
  t.Parallel()

  var greeter *Greeter

  coretest.Start(t, core.New(greet.Module), fx.Populate(&greeter))

  assert.Equal(t, "hello oryn", greeter.Greet(t.Context(), "oryn"))
}

Function	Description
coretest.Start(t, app, options...)	Builds and starts the application, and stops it when the test ends
coretest.New(t, app, options...)	Builds the application without starting it
coretest.TestOptions()	The options added to every test application, to build an fx.App yourself

The options come after the application ones: get dependencies with fx.Populate, replace them with fx.Replace or fx.Decorate, and override the configuration with config.AsOptions:

coretest.Start(t, app,
  config.AsOptions(config.WithValues(map[string]any{"log.level": "debug"})),
  fx.Decorate(func() Clock { return fakeClock }),
  fx.Populate(&service),
)

The application uses the test context as base context: it is cancelled when the test ends.

Assert telemetry

The in-memory exporters are in the container. Assert on them with the otel/oteltest packages:

func TestCheckout(t *testing.T) {
  t.Parallel()

  var (
    service *CheckoutService
    spans   *tracetest.InMemoryExporter
    logs    *logtest.InMemoryExporter
    metrics *sdkmetric.ManualReader
  )

  coretest.Start(t, app, fx.Populate(&service, &spans, &logs, &metrics))

  require.NoError(t, service.Checkout(t.Context(), cart))

  spantest.HasSpan(t, spans, spantest.WithName("checkout"))
  logtest.HasRecord(t, logs, logtest.WithBody("checked out"), logtest.WithLevel(slog.LevelInfo))
  assert.Equal(t, int64(1), metrictest.Int64Sum(t, metrics, "checkout.orders"))
}

Package	Assertions	Filters
spantest	HasSpan, HasNoSpan, SpanCount, Find	WithName, WithNameContains, WithKind, WithStatus, WithAttribute, WithAttributeValue, WithParent
logtest	HasRecord, HasNoRecord, RecordCount	WithBody, WithBodyContains, WithLevel, WithSeverity, WithAttribute, WithAttributeValue
metrictest	HasMetric, HasNoMetric, Int64Sum, Collect, Find	WithName, WithUnit, WithAttributeValue

When an assertion fails, the message lists what was recorded, to see what went wrong without debugging.

Test failures to start

To test that an application fails to start, build it with fx.New and check the error:

app := fx.New(core.New(myModule).Options(coretest.TestOptions(), fx.NopLogger)...)
require.ErrorContains(t, app.Err(), "invalid configuration")