diff --git a/tests/test_helpers.bash b/tests/test_helpers.bash
index 9990049..4ee7ed9 100644
--- a/tests/test_helpers.bash
+++ b/tests/test_helpers.bash
@@ -9,7 +9,7 @@
 function assert {
     local expected_output=$1
     shift
-    actual_output=$("$@")
+    local actual_output=$("$@")
     if ! [ "$actual_output" = "$expected_output" ]; then
         echo "expected: \"$expected_output\", actual: \"$actual_output\""
         false
@@ -55,3 +55,8 @@
         false
     fi
 }
+
+function cleanup {
+    docker kill $1 &>/dev/null ||:
+    docker rm -fv $1 &>/dev/null ||:
+}