tests(app): 🧼 decompose init_chain.rs test file

this was useful in early development, but we can (a) break this into
distinct test files, and (b) get rid of
`mock_consensus_can_send_an_init_chain_request` which is now obselete
thanks to a more sophisticated test suite.

crates/core/app/tests/mock_consensus_can_define_a_genesis_validator.rs

@@ -0,0 +1,58 @@
+use {
+    self::common::BuilderExt,
+    anyhow::anyhow,
+    cnidarium::TempStorage,
+    penumbra_app::{genesis::AppState, server::consensus::Consensus},
+    penumbra_mock_consensus::TestNode,
+    penumbra_stake::component::validator_handler::ValidatorDataRead as _,
+    tap::{Tap, TapFallible},
+    tracing::info,
+};
+
+mod common;
+
+/// Exercises that the mock consensus engine can provide a single genesis validator.
+#[tokio::test]
+async fn mock_consensus_can_define_a_genesis_validator() -> anyhow::Result<()> {
+    // Install a test logger, acquire some temporary storage, and start the test node.
+    let guard = common::set_tracing_subscriber();
+    let storage = TempStorage::new().await?;
+    let test_node = {
+        let app_state = AppState::default();
+        let consensus = Consensus::new(storage.as_ref().clone());
+        TestNode::builder()
+            .single_validator()
+            .with_penumbra_auto_app_state(app_state)?
+            .init_chain(consensus)
+            .await
+            .tap_ok(|e| tracing::info!(hash = %e.last_app_hash_hex(), "finished init chain"))?
+    };
+
+    let snapshot = storage.latest_snapshot();
+    let validators = snapshot
+        .validator_definitions()
+        .tap(|_| info!("getting validator definitions"))
+        .await?;
+    match validators.as_slice() {
+        [v] => {
+            let identity_key = v.identity_key;
+            let status = snapshot
+                .get_validator_state(&identity_key)
+                .await?
+                .ok_or_else(|| anyhow!("could not find validator status"))?;
+            assert_eq!(
+                status,
+                penumbra_stake::validator::State::Active,
+                "validator should be active"
+            );
+        }
+        unexpected => panic!("there should be one validator, got: {unexpected:?}"),
+    }
+
+    // Free our temporary storage.
+    drop(test_node);
+    drop(storage);
+    drop(guard);
+
+    Ok(())
+}

crates/core/app/tests/mock_consensus_can_send_a_sequence_of_empty_blocks.rs

@@ -0,0 +1,43 @@
+use {
+    self::common::BuilderExt,
+    cnidarium::TempStorage,
+    penumbra_app::{genesis::AppState, server::consensus::Consensus},
+    penumbra_mock_consensus::TestNode,
+    penumbra_sct::component::clock::EpochRead as _,
+    tap::TapFallible,
+};
+
+mod common;
+
+/// Exercises that a series of empty blocks, with no validator set present, can be successfully
+/// executed by the consensus service.
+#[tokio::test]
+async fn mock_consensus_can_send_a_sequence_of_empty_blocks() -> anyhow::Result<()> {
+    // Install a test logger, acquire some temporary storage, and start the test node.
+    let guard = common::set_tracing_subscriber();
+    let storage = TempStorage::new().await?;
+    let mut test_node = {
+        let app_state = AppState::default();
+        let consensus = Consensus::new(storage.as_ref().clone());
+        TestNode::builder()
+            .single_validator()
+            .with_penumbra_auto_app_state(app_state)?
+            .init_chain(consensus)
+            .await
+            .tap_ok(|e| tracing::info!(hash = %e.last_app_hash_hex(), "finished init chain"))?
+    };
+
+    let height = || async { storage.latest_snapshot().get_block_height().await };
+
+    // Fast forward eight blocks, and show that the height is 8 after doing so.
+    assert_eq!(height().await?, 0, "height should begin at 0");
+    test_node.fast_forward(8).await?;
+    assert_eq!(height().await?, 8_u64, "height should grow");
+
+    // Free our temporary storage.
+    drop(test_node);
+    drop(storage);
+    drop(guard);
+
+    Ok(())
+}