tests: 🤝 hoist test subscriber into a standalone library (#4200)

in #4193, @zbuc is working on some changes to the dex component. in the
`penumbra-app` crate, we have a helpful utility to define a tracing
subscriber that correctly interacts with `libtest`'s output capturing,
and can be configured via `RUST_LOG` when running tests.

this is a tremendously helpful aid in debugging issues during feature
development, and is not specific to the `penumbra-app` crate.

this commit hoists that test utility into a standalone library in
`crates/test/`, so that other components like the dex can also create a
guard to capture traces in tests.

now we can share this, by doing this:

```rust
 #[tokio::test]
 async fn example_test_case() -> anyhow::Result<()> {
     // Install a test logger...
     let guard = set_tracing_subscriber();

     // Test logic here...

     drop(guard);
     Ok(())
 }
```

#### checklist before requesting a review

- [x] If this code contains consensus-breaking changes, I have added the
"consensus-breaking" label. Otherwise, I declare my belief that there
are not consensus-breaking changes, for the following reason:

  > only changes test code

Cargo.toml

@@ -45,6 +45,7 @@ members = [
   "crates/test/mock-client",
   "crates/test/mock-consensus",
   "crates/test/tct-property-test",
+  "crates/test/tracing-subscriber",
   "crates/util/auto-https",
   "crates/util/tendermint-proxy",
   "crates/util/tower-trace",
@@ -179,6 +180,7 @@ penumbra-sct                     = { default-features = false, path = "crates/co
 penumbra-shielded-pool           = { default-features = false, path = "crates/core/component/shielded-pool" }
 penumbra-stake                   = { default-features = false, path = "crates/core/component/stake" }
 penumbra-tct                     = { default-features = false, path = "crates/crypto/tct" }
+penumbra-test-subscriber         = { path = "crates/test/tracing-subscriber" }
 penumbra-transaction             = { default-features = false, path = "crates/core/transaction" }
 penumbra-txhash                  = { default-features = false, path = "crates/core/txhash" }
 penumbra-view                    = { path = "crates/view" }

crates/core/app/Cargo.toml

@@ -81,14 +81,15 @@ tracing                          = { workspace = true }
 url                              = { workspace = true }
 
 [dev-dependencies]
-ed25519-consensus       = { workspace = true }
-penumbra-mock-consensus = { workspace = true }
-penumbra-mock-client    = { workspace = true }
-rand                    = { workspace = true }
-rand_core               = { workspace = true }
-rand_chacha             = { workspace = true }
-tap                     = { workspace = true }
-tracing-subscriber      = { workspace = true }
+ed25519-consensus        = { workspace = true }
+penumbra-mock-consensus  = { workspace = true }
+penumbra-mock-client     = { workspace = true }
+penumbra-test-subscriber = { workspace = true }
+rand                     = { workspace = true }
+rand_core                = { workspace = true }
+rand_chacha              = { workspace = true }
+tap                      = { workspace = true }
+tracing-subscriber       = { workspace = true }
 
 # Enable the feature flags to get proving keys when running tests.
 [dev-dependencies.penumbra-proof-params]

crates/core/app/tests/common/mod.rs

@@ -2,9 +2,12 @@
 
 // NB: these reëxports are shared and consumed by files in `tests/`.
 #[allow(unused_imports)]
-pub use self::{
-    temp_storage_ext::TempStorageExt, test_node_builder_ext::BuilderExt,
-    test_node_ext::TestNodeExt, tracing_subscriber::set_tracing_subscriber,
+pub use {
+    self::{
+        temp_storage_ext::TempStorageExt, test_node_builder_ext::BuilderExt,
+        test_node_ext::TestNodeExt,
+    },
+    penumbra_test_subscriber::set_tracing_subscriber,
 };
 
 /// Penumbra-specific extensions to the mock consensus builder.
@@ -19,9 +22,3 @@ mod temp_storage_ext;
 ///
 /// See [`TestNodeExt`].
 mod test_node_ext;
-
-/// A pretty [`tracing`] subscriber for use in test cases.
-///
-/// NB: this subscriber makes use of a test writer, that is compatible with `cargo test`'s output
-/// capturing.
-mod tracing_subscriber;

crates/test/tracing-subscriber/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "penumbra-test-subscriber"
+authors.workspace = true
+edition.workspace = true
+version.workspace = true
+repository.workspace = true
+homepage.workspace = true
+license.workspace = true
+publish = false
+
+[dependencies]
+tracing = { workspace = true }
+tracing-subscriber = { workspace = true }

crates/core/app/tests/common/tracing_subscriber.rs → crates/test/tracing-subscriber/src/lib.rs

@@ -1,3 +1,8 @@
+//! A pretty [`tracing`] subscriber for use in test cases.
+//!
+//! NB: this subscriber makes use of a test writer, that is compatible with `cargo test`'s output
+//! capturing.
+
 use {
     tracing::subscriber::{set_default, DefaultGuard},
     tracing_subscriber::{filter::EnvFilter, fmt},