diff --git a/stateless/test_fuzz.nim b/stateless/test_fuzz.nim
new file mode 100644
index 000000000..6ed5176fb
--- /dev/null
+++ b/stateless/test_fuzz.nim
@@ -0,0 +1,15 @@
+import
+  testutils/fuzzing, eth/trie/db,
+  ./tree_from_witness, ./witness_types
+
+# please read instruction in status-im/nim-testutils/fuzzing/readme.md
+# or status-im/nim-testutils/fuzzing/fuzzing_on_windows.md
+# if you want to run fuzz test
+
+test:
+  var db = newMemoryDB()
+  try:
+    var tb = initTreeBuilder(payload, db, {wfEIP170})
+    let root = tb.buildTree()
+  except ParsingError, ContractCodeError:
+    debugEcho "Error detected ", getCurrentExceptionMsg()
diff --git a/stateless/test_witness_json.nim b/stateless/test_witness_json.nim
index 63d80440d..52d5c9999 100644
--- a/stateless/test_witness_json.nim
+++ b/stateless/test_witness_json.nim
@@ -1,6 +1,6 @@
 import
-  eth/common, eth/trie/db, json, os, unittest,
-  ../stateless/[tree_from_witness],
+  eth/common, eth/trie/db, json, os, unittest2,
+  ./tree_from_witness, parseopt,
   ./witness_types, stew/byteutils
 
 type
@@ -99,7 +99,7 @@ proc processNode(t: var Tester, x: JsonNode, storageMode: bool = false) =
 proc parseRootHash(x: string): KeccakHash =
   result.data = hexToByteArray[32](x)
 
-proc parseTester(t: var Tester, n: JsonNode) =
+proc parseTester(t: var Tester, n: JsonNode, testStatusIMPL: var TestStatus) =
   t.error = n["error"].getBool()
   t.rootHash = parseRootHash(n["rootHash"].getStr())
   t.write(n["version"])
@@ -112,13 +112,13 @@ proc parseTester(t: var Tester, n: JsonNode) =
   except ParsingError:
     check t.error == true
 
-proc parseTester(filename: string): Tester =
+proc parseTester(filename: string, testStatusIMPL: var TestStatus): Tester =
   let n = parseFile(filename)
-  parseTester(result, n)
+  parseTester(result, n, testStatusIMPL)
 
 proc runTest(filePath, fileName: string) =
   test fileName:
-    let t = parseTester(filePath)
+    let t = parseTester(filePath, testStatusIMPL)
     var db = newMemoryDB()
     try:
       var tb = initTreeBuilder(t.output, db, {wfEIP170})
@@ -129,13 +129,48 @@ proc runTest(filePath, fileName: string) =
         check root == t.rootHash
         check t.error == false
     except ParsingError, ContractCodeError:
-      debugEcho "Error detected ", getCurrentExceptionMsg()
+      echo "Exception detected ", getCurrentExceptionMsg()
       check t.error == true
 
+proc writeFuzzData(filePath, fileName: string) =
+  var testStatusIMPL: TestStatus
+  let t = parseTester(filePath, testStatusIMPL)
+  var db = newMemoryDB()
+  var tb = initTreeBuilder(t.output, db, {wfEIP170})
+  let root = tb.buildTree()
+  writeFile(filename, t.output)
+
+proc fuzzTool(): bool =
+  var filename: string
+  var numArg = 0
+
+  for kind, key, val in getopt():
+    case kind
+    of cmdArgument:
+      inc numArg
+      case numArg
+      of 1:
+        if key != "fuzz":
+          quit(1)
+      of 2:
+        filename = key
+      else:
+        discard
+    of cmdLongOption, cmdShortOption:
+      discard
+    of cmdEnd: assert(false) # cannot happen
+
+  if filename != "":
+    echo "generate fuzz data"
+    writeFuzzData(filename, "fuzz.data")
+    return true
+
 proc witnessJsonMain*() =
-  for x in walkDirRec("stateless" / "fixtures"):
-    let y = splitPath(x)
-    runTest(x, y.tail)
+  suite "test tree builder against json fixtures":
+    for x in walkDirRec("stateless" / "fixtures"):
+      let y = splitPath(x)
+      runTest(x, y.tail)
 
 when isMainModule:
-  witnessJsonMain()
+  if not fuzzTool():
+    witnessJsonMain()
diff --git a/stateless/test_witness_keys.nim b/stateless/test_witness_keys.nim
index 5458da586..93e160916 100644
--- a/stateless/test_witness_keys.nim
+++ b/stateless/test_witness_keys.nim
@@ -1,5 +1,5 @@
 import
-  randutils, random, unittest, stew/byteutils,
+  randutils, random, unittest2, stew/byteutils,
   eth/[common, rlp], eth/trie/[hexary, db, trie_defs, nibbles],
   faststreams/inputs, nimcrypto/sysrand,
   ../stateless/[witness_from_tree, tree_from_witness],
diff --git a/tests/all_tests.nim b/tests/all_tests.nim
index 7bbdf0a99..6b8a38a4d 100644
--- a/tests/all_tests.nim
+++ b/tests/all_tests.nim
@@ -11,12 +11,12 @@ import threadpool
 # AppVeyor may go out of memory with the default of 4
 setMinPoolSize(2)
 
-proc executeMyself(numModules: int): int =
+proc executeMyself(numModules: int, names: openArray[string]): int =
   let appName = getAppFilename()
   for i in 0..<numModules:
     let execResult = execCmd(appName & " " & $i)
     if execResult != 0:
-      stderr.writeLine("subtest no: " & $i & " failed")
+      stderr.writeLine("subtest no: " & $i & " failed: " & names[i])
     result = result or execResult
 
 proc getImportStmt(stmtList: NimNode): NimNode =
@@ -35,9 +35,16 @@ proc ofStmt(idx: int, singleModule: NimNode): NimNode =
     newCall(moduleMain)
   )
 
+proc toModuleNames(importStmt: NimNode): NimNode =
+  result = nnkBracket.newTree
+  for singleModule in importStmt:
+    let x = normalize(singleModule.toStrLit.strVal)
+    result.add newLit(x)
+
 macro cliBuilder(stmtList: typed): untyped =
   let importStmt = stmtList.getImportStmt
   let moduleCount = importStmt.len
+  let moduleNames = importStmt.toModuleNames
 
   # case paramStr(1).parseInt
   var caseStmt = nnkCaseStmt.newTree(
@@ -59,7 +66,8 @@ macro cliBuilder(stmtList: typed): untyped =
 
   result = quote do:
     if paramCount() == 0:
-      quit(executeMyself(`moduleCount`))
+      const names = `moduleNames`
+      quit(executeMyself(`moduleCount`, names))
     else:
       disableParamFiltering()
       `caseStmt`
@@ -103,4 +111,3 @@ cliBuilder:
           ../stateless/test_witness_keys,
           ../stateless/test_block_witness,
           ../stateless/test_witness_json
-