Add test for isort skip file functionality

Author: aseembits93

tests/test_formatter.py

@@ -796,4 +796,12 @@ def _is_valid(self, item):
     optimization_function = """def process(self,data):
         '''Single quote docstring with formatting issues.'''
         return{'result':[item for item in data if self._is_valid(item)]}"""
-    _run_formatting_test(source_code, True, optimized_function=optimization_function, expected=expected)
+    _run_formatting_test(source_code, True, optimized_function=optimization_function, expected=expected)
+
+def test_sort_imports_skip_file():
+    """Test that isort skips files with # isort:skip_file."""
+    code = """# isort:skip_file
+
+import sys, os, json  # isort will ignore this file completely"""
+    new_code = sort_imports(code)
+    assert new_code == code