tests: Added tests for each SubintentStructureError

radix-transactions/src/manifest/manifest_instructions.rs

@@ -1341,6 +1341,14 @@ pub struct YieldToParent {
     pub args: ManifestValue,
 }
 
+impl YieldToParent {
+    pub fn empty() -> Self {
+        Self {
+            args: ManifestValue::unit(),
+        }
+    }
+}
+
 impl ManifestInstruction for YieldToParent {
     const IDENT: &'static str = "YIELD_TO_PARENT";
     const ID: u8 = INSTRUCTION_YIELD_TO_PARENT_DISCRIMINATOR;

radix-transactions/src/model/v1/blobs.rs

@@ -11,6 +11,12 @@ pub struct BlobsV1 {
     pub blobs: Vec<BlobV1>,
 }
 
+impl BlobsV1 {
+    pub fn none() -> Self {
+        Self { blobs: Vec::new() }
+    }
+}
+
 impl From<IndexMap<Hash, Vec<u8>>> for BlobsV1 {
     fn from(blobs: IndexMap<Hash, Vec<u8>>) -> Self {
         let blobs = blobs

radix-transactions/src/model/v2/child_subintent_hashes_v2.rs

@@ -35,6 +35,12 @@ impl ChildSubintentSpecifier {
     }
 }
 
+impl From<SubintentHash> for ChildSubintentSpecifier {
+    fn from(hash: SubintentHash) -> Self {
+        Self { hash }
+    }
+}
+
 /// A new-type representing the index of a referenced intent.
 /// The first few of these will be the children of the given intent.
 ///

radix-transactions/src/model/v2/intent_signatures_v2.rs

@@ -7,6 +7,18 @@ pub struct IntentSignaturesV2 {
     pub signatures: Vec<IntentSignatureV1>,
 }
 
+impl IntentSignaturesV2 {
+    pub fn none() -> Self {
+        Self {
+            signatures: Vec::new(),
+        }
+    }
+
+    pub fn new(signatures: Vec<IntentSignatureV1>) -> Self {
+        Self { signatures }
+    }
+}
+
 impl TransactionPartialPrepare for IntentSignaturesV2 {
     type Prepared = PreparedIntentSignaturesV2;
 }

radix-transactions/src/validation/mod.rs

@@ -16,4 +16,4 @@ pub use transaction_structure_validator::*;
 pub use transaction_validation_configuration::*;
 pub use transaction_validator::*;
 #[cfg(test)]
-pub use validation_test_helpers::*;
+pub(crate) use validation_test_helpers::*;

radix-transactions/src/validation/transaction_structure_validator.rs

@@ -132,6 +132,9 @@ impl TransactionValidator {
         // We also:
         // * Save the unique parent on each subintent which is a child
         // * Save the children of an intent into its intent details
+        //
+        // After this step, we know that each subintent has at most one parent.
+        // We determine that every subintent has exactly one parent in step 4.
 
         // STEP 2A - Handle children of the root intent
         {
@@ -186,8 +189,14 @@ impl TransactionValidator {
         // We traverse the child relationships from the root, and mark a depth.
         // We error if any exceed the maximum depth.
         //
-        // As each child has at most one parent, we can guarantee the work is bounded
-        // by the total number of subintents.
+        // The iteration count is guaranteed to be bounded by the number of subintents because:
+        // * Each subintent has at most one parent from step 2.
+        // * Each parent -> child relationship is traversed at most once in the iteration.
+        //   Quick proof by contradiction:
+        //   - Assume not. Then some parent A is visited more than once.
+        //   - Take the earliest such A in the iteration.
+        //   - On both of its visits, A can only have been visited from its parent B.
+        //   - But then B must have been visited more than once, contradicting the minimality of A.
         let mut work_list = vec![];
         for index in root_intent_details.children.iter() {
             work_list.push((*index, 1));
@@ -224,8 +233,8 @@ impl TransactionValidator {
         // * Every subintent has a unique parent.
         // * Every subintent is reachable from the root.
         //
-        // Therefore there is a unique path from every subintent to the root
-        // So we have confirmed the subintents form a tree.
+        // Therefore there is a unique path from every subintent to the root, which implies
+        // the subintents form a tree.
         for (hash, details) in non_root_subintent_details.iter() {
             if details.depth == 0 {
                 return Err(