diff --git a/tests/requirements.txt b/tests/requirements.txt
index 9955dec..e7c049e 100644
--- a/tests/requirements.txt
+++ b/tests/requirements.txt
@@ -1,2 +1,8 @@
+# Test-only deps. boto3/pandas/awswrangler are NOT in the Lambda packages
+# (they come from the SDK-for-pandas layer + runtime), but the handler/slackio
+# modules import them at load time, so they're needed to import-and-test here.
 pytest
 pytest-cov
+boto3
+pandas
+awswrangler