diff --git a/SprintLib/testers/BaseTester.py b/SprintLib/testers/BaseTester.py
index e617af9..98c77e2 100644
--- a/SprintLib/testers/BaseTester.py
+++ b/SprintLib/testers/BaseTester.py
@@ -40,7 +40,7 @@ class BaseTester:
         result = open(join(self.solution.testing_directory, "output.txt"), "r").read().strip().replace('\r\n', '\n')
         print("got result", result)
         if exists(join(self.path, "checker.py")):
-            self.solution.exec_command(f"cp {filename}.a expected.txt")
+            copyfile(join(self.path, filename + '.a'), join(self.path, 'expected.txt'))
             call(f"docker run --name solution_{self.solution.id}_checker --volume=/sprint-data/solutions/{self.solution.id}:/app -t -d python:3.6", shell=True)
             code = call(f'docker exec -i solution_{self.solution.id}_checker sh -c "cd app && python checker.py"', shell=True, timeout=1)
             if code != 0: