Testing Your Agent

An agent built on yoagent can be tested without a network or an API key: MockProvider plays the model, returning scripted responses one turn at a time, and everything else (the loop, your tools, middleware, events) runs for real. The examples below are compiled and run as tests/testing_guide_test.rs.

A scripted run

Give MockProvider the turns you expect, pair it with ModelConfig::mock(), and assert on the events or the final history:

#![allow(unused)]
fn main() {
use yoagent::provider::mock::{MockResponse, MockToolCall};
use yoagent::provider::{MockProvider, ModelConfig};
use yoagent::*;

#[tokio::test]
async fn the_agent_calls_the_tool_then_answers() {
    // Each response is one model turn, in order.
    let provider = MockProvider::new(vec![
        MockResponse::ToolCalls(vec![MockToolCall {
            name: "echo".into(),
            arguments: serde_json::json!({"text": "hi"}),
            provider_metadata: None,
        }]),
        MockResponse::Text("The tool said hi.".into()),
    ]);
    let mut agent =
        Agent::from_provider(provider, ModelConfig::mock()).with_tools(vec![Box::new(Echo)]);

    let mut rx = agent.prompt("say hi through the tool").await;
    let mut tool_output = None;
    while let Some(event) = rx.recv().await {
        if let AgentEvent::ToolExecutionEnd { result, .. } = event {
            tool_output = result.content.first().cloned();
        }
    }
    agent.finish().await;

    assert!(matches!(tool_output, Some(Content::Text { text }) if text == "hi"));
}
}

Echo is an ordinary AgentTool; the test file has it in full. For a single text answer, MockProvider::text("…") is enough.

MockProvider also checks that every request pairs tool calls with their results (no unanswered call, no stray result, nothing in between), the shape a real provider would reject. On a violation it panics with an explanation; under Agent::prompt that panic is in the spawned loop task, so the run ends early and your assertions on its output fail. When a malformed sequence is the point of the test, opt out: MockProvider::new(responses).without_transcript_validation().

A middleware, without an agent

ToolCallRequest::new(id, name, &args) builds the request a ToolMiddleware receives, so a policy can be tested on its own:

#![allow(unused)]
fn main() {
struct NoRm;

#[async_trait::async_trait]
impl ToolMiddleware for NoRm {
    async fn before_tool(&self, call: &ToolCallRequest<'_>) -> ToolDecision {
        let command = call.args["command"].as_str().unwrap_or("");
        if call.tool_name == "bash" && command.contains("rm ") {
            ToolDecision::Deny("no deleting".into())
        } else {
            ToolDecision::Allow
        }
    }
}

#[tokio::test]
async fn the_middleware_denies_rm() {
    let args = serde_json::json!({"command": "rm -rf build"});
    let call = ToolCallRequest::new("call-1", "bash", &args);
    assert!(matches!(NoRm.before_tool(&call).await, ToolDecision::Deny(_)));
}
}

When the policy depends on what the user asked, give the request that context: .with_run_prompts(&prompts) for the run's prompts, or .with_messages(&history) for the whole conversation. A policy should read call.user_request_parts(); user_request() is prose whose format may change.

Abort

abort() cancels the run; finish() waits for it and leaves the agent usable. This shows the call pattern — with an instant mock the run may well finish before the abort lands:

#![allow(unused)]
fn main() {
#[tokio::test]
async fn an_abort_ends_the_run() {
    let mut agent = Agent::from_provider(MockProvider::text("hello"), ModelConfig::mock());
    let mut rx = agent.prompt("hi").await;
    agent.abort();
    while rx.recv().await.is_some() {}
    agent.finish().await;
    assert!(!agent.is_streaming());
}
}

Beyond the mock

• Streaming and provider quirks are tested against a local HTTP server (wiremock) serving hand-built bodies in each provider's wire format (SSE; binary event stream for Bedrock) — see tests/*_stream_test.rs in the repository.
• Live runs belong in an example run on demand, not in cargo test: the repository's examples/release_smoke.rs checks a real provider end to end.