Revise userName error result

Author: rocky

mathics/builtin/system.py

@@ -401,7 +401,7 @@ class UserName(Predefined):
     </dl>
 
     X> $UserName
-     = rocky
+     = ...
     """
 
     name = "$UserName"
@@ -410,7 +410,7 @@ def evaluate(self, evaluation) -> String:
         try:
             return String(os.getlogin())
         except:
-            return String("rocky")
+            return String("??user-retrieval-error")
 
 
 class Version(Predefined):

test/test_file.py

@@ -0,0 +1,30 @@
+from mathics.core.parser import parse, MathicsSingleLineFeeder
+from mathics.core.definitions import Definitions
+from mathics.core.evaluation import Evaluation
+import pytest
+
+
+definitions = Definitions(add_builtin=True)
+evaluation = Evaluation(definitions=definitions, catch_interrupt=False)
+
+
+def _evaluate(str_expression):
+    expr = parse(definitions, MathicsSingleLineFeeder(str_expression))
+    return expr.evaluate(evaluation)
+
+
+def test_get_and_put():
+    temp_directory = _evaluate("$TemporaryDirectory").to_python()
+    if len(temp_directory)<3:
+        return
+    temp_directory = temp_directory[1:-1]
+    temp_filename = f"{temp_directory}/testfile"
+    print(temp_filename)
+    result = _evaluate(f"40! >> {temp_filename}").to_python()
+    assert result is None
+
+    result = _evaluate(f"<< {temp_filename}")
+    assert result == _evaluate("40!")
+
+    result = _evaluate(f"DeleteFile[\"{temp_filename}\"]").to_python()
+    assert result is None