Handle missing slasher backend in tests

Author: paulhauner

beacon_node/beacon_chain/tests/block_verification.rs

@@ -987,9 +987,23 @@ async fn block_gossip_verification() {
 #[tokio::test]
 async fn verify_block_for_gossip_slashing_detection() {
     let slasher_dir = tempdir().unwrap();
-    let slasher = Arc::new(
-        Slasher::open(SlasherConfig::new(slasher_dir.path().into()), test_logger()).unwrap(),
-    );
+
+    let slasher_result =
+        Slasher::open(SlasherConfig::new(slasher_dir.path().into()), test_logger());
+
+    // The slasher should only instantiate if a backend feature-flag has been
+    // provided.
+    //
+    // For example: `--features slasher/lmdb`
+    let slasher = if cfg!(any(feature = "mdbx", feature = "lmdb")) {
+        Arc::new(slasher_result.unwrap())
+    } else {
+        assert!(matches!(
+            slasher_result,
+            Err(slasher::Error::SlasherDatabaseBackendDisabled)
+        ));
+        return;
+    };
 
     let inner_slasher = slasher.clone();
     let harness = BeaconChainHarness::builder(MainnetEthSpec)