Added additional tests to cover HexaryTrie MPT proofs. (#650)

* Added additional tests to cover HexaryTrie MPT proofs.

* Minor updates based on PR comments.

tests/trie/test_hexary_proof.nim

@@ -10,10 +10,11 @@
 {.push raises: [].}
 
 import
+  std/sequtils,
   unittest2,
   stint,
-  std/sequtils,
   nimcrypto/hash,
+  stew/byteutils,
   ../../eth/trie/[hexary, db, trie_defs, hexary_proof_verification]
 
 proc getKeyBytes(i: int): seq[byte] =
@@ -59,3 +60,87 @@ suite "MPT trie proof verification":
 
     check:
       res.isMissing()
+
+  # The following test cases were copied from the Rust hexary trie implementation.
+  # See here: https://github.com/citahub/cita_trie/blob/master/src/tests/mod.rs#L554
+  test "Validate proof for empty trie":
+    let db = newMemoryDB()
+    var trie = initHexaryTrie(db)
+
+    let
+      proof = trie.getBranch("not-exist".toBytes)
+      res = verifyMptProof(proof, trie.rootHash, "not-exist".toBytes, "not-exist".toBytes)
+
+    check:
+      trie.rootHash == keccakHash(emptyRlp)
+      proof.len() == 1 # Note that the Rust implementation returns an empty list for this scenario
+      proof == @[emptyRlp]
+      res.kind == InvalidProof
+
+  test "Validate proof for one element trie":
+    let db = newMemoryDB()
+    var trie = initHexaryTrie(db)
+
+    trie.put("k".toBytes, "v".toBytes)
+
+    let
+      rootHash = trie.rootHash
+      proof = trie.getBranch("k".toBytes)
+      res = verifyMptProof(proof, rootHash, "k".toBytes, "v".toBytes)
+
+    check:
+      proof.len() == 1
+      res.isValid()
+
+    # removing key does not affect the verify process
+    trie.del("k".toBytes)
+    check verifyMptProof(proof, rootHash, "k".toBytes, "v".toBytes).isValid()
+
+  test "Validate proof bytes":
+    let db = newMemoryDB()
+    var trie = initHexaryTrie(db)
+
+    trie.put("doe".toBytes, "reindeer".toBytes)
+    trie.put("dog".toBytes, "puppy".toBytes)
+    trie.put("dogglesworth".toBytes, "cat".toBytes)
+
+    block:
+      let
+        rootHash = trie.rootHash
+        proof = trie.getBranch("doe".toBytes)
+        res = verifyMptProof(proof, rootHash, "doe".toBytes, "reindeer".toBytes)
+
+      check:
+        to0xHex(rootHash.data) == "0x8aad789dff2f538bca5d8ea56e8abe10f4c7ba3a5dea95fea4cd6e7c3a1168d3"
+        proof.len() == 3
+        proof[0] == "e5831646f6a0db6ae1fda66890f6693f36560d36b4dca68b4d838f17016b151efe1d4c95c453".hexToSeqByte
+        proof[1] == "f83b8080808080ca20887265696e6465657280a037efd11993cb04a54048c25320e9f29c50a432d28afdf01598b2978ce1ca3068808080808080808080".hexToSeqByte
+        res.isValid()
+
+    block:
+      let
+        proof = trie.getBranch("dogg".toBytes)
+        res = verifyMptProof(proof, trie.rootHash, "dogg".toBytes, "puppy".toBytes)
+
+      check:
+        proof.len() == 4
+        proof[0] == "e5831646f6a0db6ae1fda66890f6693f36560d36b4dca68b4d838f17016b151efe1d4c95c453".hexToSeqByte
+        proof[1] == "f83b8080808080ca20887265696e6465657280a037efd11993cb04a54048c25320e9f29c50a432d28afdf01598b2978ce1ca3068808080808080808080".hexToSeqByte
+        proof[2] == "e4808080808080ce89376c6573776f72746883636174808080808080808080857075707079".hexToSeqByte
+        res.isMissing()
+
+    block:
+      let
+        proof = newSeq[seq[byte]]()
+        res = verifyMptProof(proof, trie.rootHash, "doe".toBytes, "reindeer".toBytes)
+
+      check res.kind == InvalidProof
+
+    block:
+      let
+        proof = @["aaa".toBytes, "ccc".toBytes]
+        res = verifyMptProof(proof, trie.rootHash, "doe".toBytes, "reindeer".toBytes)
+
+      check res.kind == InvalidProof
+
+