Add Frontier::random_of_size to facilitate testing.

incrementalmerkletree/Cargo.toml

@@ -20,9 +20,13 @@ rustdoc-args = ["--cfg", "docsrs"]
 [dependencies]
 either = "1.8"
 proptest = { version = "1.0.0", optional = true }
+rand = { version = "0.8", optional = true }
+rand_core = { version = "0.6", optional = true }
 
 [dev-dependencies]
 proptest = "1.0.0"
+rand = "0.8"
+rand_core = "0.6"
 
 [features]
 # The legacy-api feature guards types and functions that were previously
@@ -31,4 +35,4 @@ proptest = "1.0.0"
 legacy-api = []
 # The test-dependencies feature guards types and functions that are
 # useful for testing incremental Merkle trees and Merkle tree frontiers.
-test-dependencies = ["proptest"]
+test-dependencies = ["dep:proptest", "dep:rand", "dep:rand_core"]

incrementalmerkletree/src/frontier.rs

@@ -6,6 +6,12 @@ use crate::{Address, Hashable, Level, MerklePath, Position, Source};
 #[cfg(feature = "legacy-api")]
 use {std::collections::VecDeque, std::iter::repeat};
 
+#[cfg(any(test, feature = "test-dependencies"))]
+use rand::{
+    distributions::{Distribution, Standard},
+    Rng, RngCore,
+};
+
 /// Validation errors that can occur during reconstruction of a Merkle frontier from
 /// its constituent parts.
 #[derive(Clone, Debug, PartialEq, Eq)]
@@ -287,6 +293,29 @@ impl<H: Hashable + Clone, const DEPTH: u8> Frontier<H, DEPTH> {
     }
 }
 
+#[cfg(any(test, feature = "test-dependencies"))]
+impl<H: Hashable + Clone, const DEPTH: u8> Frontier<H, DEPTH>
+where
+    Standard: Distribution<H>,
+{
+    /// Generates a random frontier of a Merkle tree having the specified size.
+    pub fn random_of_size<R: RngCore>(rng: &mut R, tree_size: u64) -> Self {
+        if tree_size == 0 {
+            Frontier::empty()
+        } else {
+            let position = tree_size.into();
+            Frontier::from_parts(
+                position,
+                rng.gen(),
+                std::iter::repeat_with(|| rng.gen())
+                    .take(position.past_ommer_count().into())
+                    .collect(),
+            )
+            .unwrap()
+        }
+    }
+}
+
 #[cfg(feature = "legacy-api")]
 #[cfg_attr(docsrs, doc(cfg(feature = "legacy-api")))]
 pub struct PathFiller<H> {