diff --git a/tests/xlfunctions/test_logical.py b/tests/xlfunctions/test_logical.py
index fb64327..4c779d4 100644
--- a/tests/xlfunctions/test_logical.py
+++ b/tests/xlfunctions/test_logical.py
@@ -54,8 +54,14 @@ def test_TRUE(self):
         self.assertTrue(logical.TRUE())
 
     def test_IFERROR(self):
-        self.assertEqual(logical.IFERROR(10/2,0),5) # Check if value is OK
-        self.assertEqual(logical.IFERROR(10/0,0),0) # Check if value cause error
-        self.assertEqual(logical.IFERROR(10/0,"ERROR"),"ERROR") # Check returning string
-        self.assertEqual(logical.IFERROR(logical.IFERROR(10/0,0) + 1,0),1) # Check nested IFERROR
-
+        num_error = xlerrors.NumExcelError()
+        div_ziro_error = xlerrors.DivZeroExcelError()
+        # Check if value is valid
+        self.assertEqual(logical.IFERROR(10 / 2, 0), 5)
+        # Check if value cause error
+        self.assertEqual(logical.IFERROR(div_ziro_error, 0), 0)
+        # Check returning string
+        self.assertEqual(logical.IFERROR(num_error, "ERROR"), "ERROR")
+        # Check nested IFERROR
+        self.assertEqual(logical.IFERROR(logical.IFERROR(div_ziro_error,
+                                                         0) + 1, 0), 1)
diff --git a/tests/xlfunctions_vs_excel/iferror_test.py b/tests/xlfunctions_vs_excel/iferror_test.py
index 9713a8b..47fbbb4 100644
--- a/tests/xlfunctions_vs_excel/iferror_test.py
+++ b/tests/xlfunctions_vs_excel/iferror_test.py
@@ -1,7 +1,5 @@
 from .. import testing
 
-from xlcalculator.xlfunctions import xlerrors
-
 
 class SqrtTest(testing.FunctionalTestCase):
     filename = "IFERROR.xlsx"
@@ -17,19 +15,19 @@ def test_evaluation_C2(self):
             self.evaluator.get_cell_value('Sheet1!C2!'),
             self.evaluator.evaluate('Sheet1!C2')
         )
-    
+
     def test_evaluation_C3(self):
         self.assertEqual(
             self.evaluator.get_cell_value('Sheet1!C3!'),
             self.evaluator.evaluate('Sheet1!C3')
         )
-    
+
     def test_evaluation_C4(self):
         self.assertEqual(
             self.evaluator.get_cell_value('Sheet1!C4!'),
             self.evaluator.evaluate('Sheet1!C4')
         )
-    
+
     def test_evaluation_C5(self):
         self.assertEqual(
             self.evaluator.get_cell_value('Sheet1!C5!'),
diff --git a/xlcalculator/parser.py b/xlcalculator/parser.py
index 48bd064..ef230ac 100644
--- a/xlcalculator/parser.py
+++ b/xlcalculator/parser.py
@@ -120,7 +120,7 @@ def shunting_yard(self, raw_tokens, named_ranges, tokenize_range=False):
             for index, token in enumerate(tokens):
                 new_tokens.append(token)
 
-                if type(token.tvalue) == str:
+                if type(token.tvalue) is str:
 
                     # example -> :OFFSET( or simply :A10
                     if token.tvalue.startswith(':'):
diff --git a/xlcalculator/xlfunctions/logical.py b/xlcalculator/xlfunctions/logical.py
index 609ed5a..85b1103 100644
--- a/xlcalculator/xlfunctions/logical.py
+++ b/xlcalculator/xlfunctions/logical.py
@@ -102,12 +102,13 @@ def TRUE() -> func_xltypes.XlBoolean:
     """
     return True
 
+
 @xl.register()
 @xl.validate_args
-def IFERROR(value: func_xltypes.XlExpr,
-            value_if_error: func_xltypes.XlAnything) -> func_xltypes.XlAnything:
-    """Evaluate value, return value if has no error, otherwise return value_if_error.
-
+def IFERROR(value: func_xltypes.XlExpr, value_if_error: func_xltypes.XlAnything
+            ) -> func_xltypes.XlAnything:
+    """Evaluate value, return value if has no error,
+    otherwise return value_if_error.
     https://support.microsoft.com/en-au/office/iferror-function-c526fd07-caeb-47b8-8bb6-63f3e417f611
     """
     if isinstance(value(), xlerrors.ExcelError):