Add test for "1 / any number" expression (#786)

* Add tests for "1 / any number" expression

* Skip left number if it is 1

* Add test divide by one

tests/test_visitors/test_ast/test_operators/test_useless_math.py

@@ -164,3 +164,44 @@ def test_useful_math(
     visitor.run()
 
     assert_errors(visitor, [])
+
+
+@pytest.mark.parametrize('expression', [
+    '1 / other',
+    '1 / 11',
+    '1 / 1.1',
+])
+def test_one_to_divide(
+    assert_errors,
+    parse_ast_tree,
+    expression,
+    default_options,
+):
+    """Testing that `1 / any number` is the correct expression."""
+    tree = parse_ast_tree(expression)
+
+    visitor = UselessOperatorsVisitor(default_options, tree=tree)
+    visitor.run()
+
+    assert_errors(visitor, [])
+
+
+@pytest.mark.parametrize('expression', [
+    '1 / 1',
+    '2 / 1',
+    '3.3 / 1',
+    'other / 1',
+])
+def test_divide_by_one(
+    assert_errors,
+    parse_ast_tree,
+    expression,
+    default_options,
+):
+    """Testing an error when we divide by one."""
+    tree = parse_ast_tree(expression)
+
+    visitor = UselessOperatorsVisitor(default_options, tree=tree)
+    visitor.run()
+
+    assert_errors(visitor, [MeaninglessNumberOperationViolation])

wemake_python_styleguide/visitors/ast/operators.py

@@ -101,6 +101,9 @@ def _check_useless_math_operator(
         left: ast.AST,
         right: Optional[ast.AST] = None,
     ) -> None:
+        if isinstance(left, ast.Num) and right:
+            if left.n == 1:
+                left = None
         non_negative_numbers = self._get_non_negative_nodes(left, right)
 
         for number in non_negative_numbers: