Struct TestTrace 

pub struct TestTrace { /* private fields */ }

Main test trace collector.

Collects trace entries during test execution and can output them as structured JSON or console summary.

Implementations

impl TestTrace

pub fn new(name: impl Into<String>) -> Self

Creates a new test trace with the given name.

Example

let mut trace = TestTrace::new("client-server-flow");

pub fn builder(name: impl Into<String>) -> TestTraceBuilder

Creates a trace builder for advanced configuration.

pub fn name(&self) -> &str

Returns the trace name.

pub fn current_span_id(&self) -> Option<&str>

Returns the current span ID, if any.

pub fn log_request( &mut self, method: impl Into<String>, params: Option<&impl Serialize>, ) -> String

Logs a request.

Returns a correlation ID that can be used to match with the response.

pub fn log_response( &mut self, correlation_id: &str, result: Option<&impl Serialize>, error: Option<&impl Serialize>, )

Logs a response.

Uses the correlation ID from the matching request to calculate duration.

pub fn log_response_with_duration( &mut self, method: impl Into<String>, duration: Duration, result: Option<&impl Serialize>, error: Option<&impl Serialize>, )

Logs a response with explicit duration.

pub fn start_span(&mut self, name: impl Into<String>) -> String

Starts a new span for tracking a nested operation.

Returns the span ID.

pub fn end_span(&mut self, error: Option<&str>)

Ends the current span.

If error is provided, marks the span as failed.

pub fn end_span_by_id(&mut self, span_id: &str, error: Option<&str>)

Ends a specific span by ID.

pub fn log(&mut self, level: TraceLevel, message: impl Into<String>)

Logs a message at the specified level.

pub fn log_with_data( &mut self, level: TraceLevel, message: impl Into<String>, data: impl Serialize, )

Logs a message with additional data.

pub fn debug(&mut self, message: impl Into<String>)

Logs a debug message.

pub fn info(&mut self, message: impl Into<String>)

Logs an info message.

pub fn warn(&mut self, message: impl Into<String>)

Logs a warning message.

pub fn error(&mut self, message: impl Into<String>)

Logs an error message.

pub fn metric( &mut self, name: impl Into<String>, value: f64, unit: Option<&str>, )

Records a metric value.

pub fn add_metadata(&mut self, key: impl Into<String>, value: impl Into<Value>)

Adds custom metadata to the trace.

pub fn build_output(&self) -> TestTraceOutput

Builds the complete trace output.

pub fn save(&self, path: impl AsRef<Path>) -> Result<()>

Saves the trace to a JSON file.

Creates parent directories if they don’t exist.

Errors

Returns an error if the file cannot be written.

pub fn auto_save( &self, cleanup: Option<&TraceRetentionConfig>, ) -> Result<PathBuf>

Saves the trace with automatic file naming to the trace directory.

The file is saved to FASTMCP_TEST_TRACE_DIR/{name}_{timestamp}.json. Creates the directory if it doesn’t exist.

Optionally runs cleanup to remove old trace files.

Arguments

• cleanup - If Some, runs cleanup with the given retention config

Returns

The path to the saved file.

Errors

Returns an error if the file cannot be written.

Example

let trace = TestTrace::new("my-test");
// ... record trace entries ...

// Save with default cleanup
let path = trace.auto_save(Some(&TraceRetentionConfig::default()))?;
println!("Trace saved to: {}", path.display());

// Save without cleanup
let path = trace.auto_save(None)?;

pub fn to_json(&self) -> Result<String>

Returns the trace as a JSON string.

Errors

Returns an error if serialization fails.

pub fn print_summary(&self)

Prints a summary to stderr.

pub fn entries(&self) -> &[TraceEntry]

Returns all entries.

pub fn entry_count(&self) -> usize

Returns the number of entries.

Trait Implementations

impl Debug for TestTrace

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.