diff --git a/tests/test_torchfix.py b/tests/test_torchfix.py
index 04fb3c3..58e216c 100644
--- a/tests/test_torchfix.py
+++ b/tests/test_torchfix.py
@@ -3,8 +3,11 @@
     TorchChecker,
     TorchCodemod,
     TorchCodemodConfig,
+    DISABLED_BY_DEFAULT,
+    expand_error_codes,
     GET_ALL_VISITORS,
     GET_ALL_ERROR_CODES,
+    process_error_code_str,
 )
 import logging
 import libcst.codemod as codemod
@@ -61,3 +64,17 @@ def test_errorcodes_distinct():
         for e in error_code if isinstance(error_code, list) else [error_code]:
             assert e not in seen
             seen.add(e)
+
+
+def test_parse_error_code_str():
+    exclude_set = expand_error_codes(tuple(DISABLED_BY_DEFAULT))
+    cases = [
+        ("ALL", list(GET_ALL_ERROR_CODES())),
+        ("ALL,TOR102", list(GET_ALL_ERROR_CODES())),
+        ("TOR102", ["TOR102"]),
+        ("TOR102,TOR101", ["TOR102", "TOR101"]),
+        ("TOR1,TOR102", ["TOR102", "TOR101"]),
+        (None, list(GET_ALL_ERROR_CODES() - exclude_set)),
+    ]
+    for case, expected in cases:
+        assert expected == process_error_code_str(case)
diff --git a/torchfix/__main__.py b/torchfix/__main__.py
index 6cbdf83..de13e54 100644
--- a/torchfix/__main__.py
+++ b/torchfix/__main__.py
@@ -11,35 +11,12 @@
     TorchCodemodConfig,
     __version__ as TorchFixVersion,
     DISABLED_BY_DEFAULT,
-    expand_error_codes,
     GET_ALL_ERROR_CODES,
+    process_error_code_str,
 )
 from .common import CYAN, ENDC
 
 
-def process_error_code_str(code_str):
-    # Allow duplicates in the input string, e.g. --select ALL,TOR0,TOR001.
-    # We deduplicate them here.
-
-    # Default when --select is not provided.
-    if code_str is None:
-        exclude_set = expand_error_codes(tuple(DISABLED_BY_DEFAULT))
-        return list(GET_ALL_ERROR_CODES() - exclude_set)
-
-    raw_codes = [s.strip() for s in code_str.split(",")]
-
-    # Validate error codes
-    for c in raw_codes:
-        if len(expand_error_codes((c,))) == 0:
-            raise ValueError(f"Invalid error code: {c}, available error "
-                             f"codes: {list(GET_ALL_ERROR_CODES())}")
-
-    if "ALL" in raw_codes:
-        return list(GET_ALL_ERROR_CODES())
-
-    return list(expand_error_codes(raw_codes))
-
-
 # Should get rid of this code eventually.
 @contextlib.contextmanager
 def StderrSilencer(redirect: bool = True):
diff --git a/torchfix/torchfix.py b/torchfix/torchfix.py
index 2890196..5f28512 100644
--- a/torchfix/torchfix.py
+++ b/torchfix/torchfix.py
@@ -97,6 +97,31 @@ def get_visitors_with_error_codes(error_codes):
     return out
 
 
+def process_error_code_str(code_str):
+    # Allow duplicates in the input string, e.g. --select ALL,TOR0,TOR001.
+    # We deduplicate them here.
+
+    # Default when --select is not provided.
+    if code_str is None:
+        exclude_set = expand_error_codes(tuple(DISABLED_BY_DEFAULT))
+        return list(GET_ALL_ERROR_CODES() - exclude_set)
+
+    raw_codes = [s.strip() for s in code_str.split(",")]
+
+    # Validate error codes
+    for c in raw_codes:
+        if c == "ALL":
+            continue
+        if len(expand_error_codes((c,))) == 0:
+            raise ValueError(f"Invalid error code: {c}, available error "
+                             f"codes: {list(GET_ALL_ERROR_CODES())}")
+
+    if "ALL" in raw_codes:
+        return list(GET_ALL_ERROR_CODES())
+
+    return list(expand_error_codes(tuple(raw_codes)))
+
+
 # Flake8 plugin
 class TorchChecker:
     name = "TorchFix"