# Test Events
Nextdeck can help facilitate test-time event logs, these can be generated and captureed regardlress of the log level or
configuration of the apps logging framework, test events are accessible via "E" global command.
## Rust Setup
Add the helper as a development dependency:
```toml
[dev-dependencies]
nextdeck-helper = "0.1"
```
Emit an event from anywhere in your code:
```rust
nextdeck_helper::event!(
level: nextdeck_helper::Level::Info,
target: "artifact-cache",
"cache hit";
"key" => "docs-v2",
"source" => "local",
);
```
The short form emits an `info` event and uses the Rust module path as its target:
```rust
nextdeck_helper::event!("fixture ready"; "rows" => rows.len());
```
Field values may be any type implementing `serde::Serialize`.
The `nextdeck_helper::event` macro enter and emit only when `NEXTDECK_TEST_EVENTS` environment variable is present, it
is set by Nextdeck automatically when its running tests.
## Output Schema
Events are emitted as a single line in the form `NEXTDECK_EVENT_V1 <single-line JSON>`.
The event JSON Schema is represented below as an illustrative TypeScript type:
```ts
type TestEventV1 = {
schema_version: 1;
sequence: number; // Unsigned and monotonically increasing per process
time: number; // Unix time in milliseconds
level: "trace" | "debug" | "info" | "warn" | "error";
message: string;
pid?: number; // Include when events can come from multiple processes
thread?: string;
target?: string;
fields?: Record<string, unknown>;
source?: {
module: string;
file: string;
line: number;
};
};
```
## Source References
- [Rust event API and wire-format implementation](https://docs.rs/crate/nextdeck-helper/latest/source/src/lib.rs)
- [Test fixture using the event macro](../../tests/fixtures/output-workspace/src/lib.rs)
- [Nextdeck's event parser](../../src/test_events.rs)