Add a test that exposes our bug

Signed-off-by: mulhern <amulhern@redhat.com>

src/engine/strat_engine/pool.rs

@@ -895,6 +895,43 @@ mod tests {
         );
     }
 
+    // Verify that it is possible to add datadevs after a cache is initialized.
+    fn test_add_cachedevs_and_datadevs(paths: &[&Path]) {
+        assert!(paths.len() > 3);
+
+        let (cache_path, data_paths) = paths.split_at(1);
+        let (data_path, data_paths) = data_paths.split_at(1);
+
+        let name = "stratis-test-pool";
+        let (uuid, mut pool) =
+            StratPool::initialize(name, data_path, Redundancy::NONE, None).unwrap();
+        invariant(&pool, name);
+
+        pool.init_cache(uuid, name, cache_path).unwrap();
+        invariant(&pool, name);
+
+        pool.add_blockdevs(uuid, name, data_paths, BlockDevTier::Data)
+            .unwrap();
+
+        pool.teardown().unwrap();
+    }
+
+    #[test]
+    fn loop_test_add_cachedevs_and_datadevs() {
+        loopbacked::test_with_spec(
+            &loopbacked::DeviceLimits::Range(3, 4, None),
+            test_add_cachedevs_and_datadevs,
+        );
+    }
+
+    #[test]
+    fn real_test_add_cachedevs_and_datadevs() {
+        real::test_with_spec(
+            &real::DeviceLimits::AtLeast(3, None, None),
+            test_add_cachedevs_and_datadevs,
+        );
+    }
+
     /// Verify that adding additional blockdevs will cause a pool that is
     /// out of space to be extended.
     fn test_add_datadevs(paths: &[&Path]) {