Add a Transcript Service for testing.

Cargo.lock

@@ -2403,8 +2403,12 @@ dependencies = [
 name = "zebra-test"
 version = "0.1.0"
 dependencies = [
+ "color-eyre",
+ "futures",
  "hex",
  "lazy_static",
+ "tokio",
+ "tower",
 ]
 
 [[package]]

zebra-test/Cargo.toml

@@ -10,3 +10,9 @@ edition = "2018"
 [dependencies]
 hex = "0.4.2"
 lazy_static = "1.4.0"
+tower = "0.3.1"
+futures = "0.3.5"
+color-eyre = "0.5"
+
+[dev-dependencies]
+tokio = { version = "0.2", features = ["full"] }

zebra-test/src/lib.rs

@@ -1 +1,4 @@
+//! Miscellaneous test code for Zebra.
+
+pub mod transcript;
 pub mod vectors;

zebra-test/src/transcript.rs

@@ -0,0 +1,55 @@
+//! A [`Service`](tower::Service) implementation based on a fixed transcript.
+
+use color_eyre::eyre::{eyre, Report};
+use futures::future::{ready, Ready};
+use std::{
+    fmt::Debug,
+    task::{Context, Poll},
+};
+use tower::Service;
+
+pub struct Transcript<R, S, I>
+where
+    I: Iterator<Item = (R, S)>,
+{
+    messages: I,
+}
+
+impl<R, S, I> From<I> for Transcript<R, S, I>
+where
+    I: Iterator<Item = (R, S)>,
+{
+    fn from(messages: I) -> Self {
+        Self { messages }
+    }
+}
+
+impl<R, S, I> Service<R> for Transcript<R, S, I>
+where
+    R: Debug + Eq,
+    I: Iterator<Item = (R, S)>,
+{
+    type Response = S;
+    type Error = Report;
+    type Future = Ready<Result<S, Report>>;
+
+    fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, request: R) -> Self::Future {
+        if let Some((expected_request, response)) = self.messages.next() {
+            if request == expected_request {
+                ready(Ok(response))
+            } else {
+                ready(Err(eyre!(
+                    "Expected {:?}, got {:?}",
+                    expected_request,
+                    request
+                )))
+            }
+        } else {
+            ready(Err(eyre!("Got request after transcript ended")))
+        }
+    }
+}

zebra-test/tests/transcript.rs

@@ -0,0 +1,34 @@
+use tower::{Service, ServiceExt};
+
+use zebra_test::transcript::Transcript;
+
+const TRANSCRIPT_DATA: [(&'static str, &'static str); 4] = [
+    ("req1", "rsp1"),
+    ("req2", "rsp2"),
+    ("req3", "rsp3"),
+    ("req4", "rsp4"),
+];
+
+#[tokio::test]
+async fn transcript_returns_responses_and_ends() {
+    let mut svc = Transcript::from(TRANSCRIPT_DATA.iter().cloned());
+
+    for (req, rsp) in TRANSCRIPT_DATA.iter() {
+        assert_eq!(
+            svc.ready_and().await.unwrap().call(req).await.unwrap(),
+            *rsp,
+        );
+    }
+    assert!(svc.ready_and().await.unwrap().call("end").await.is_err());
+}
+
+#[tokio::test]
+async fn transcript_errors_wrong_request() {
+    let mut svc = Transcript::from(TRANSCRIPT_DATA.iter().cloned());
+
+    assert_eq!(
+        svc.ready_and().await.unwrap().call("req1").await.unwrap(),
+        "rsp1",
+    );
+    assert!(svc.ready_and().await.unwrap().call("bad").await.is_err());
+}