diff --git a/pytest_abra/custom_fixtures.py b/pytest_abra/custom_fixtures.py
index 972b07e..5aa86d6 100644
--- a/pytest_abra/custom_fixtures.py
+++ b/pytest_abra/custom_fixtures.py
@@ -97,10 +97,10 @@ def URL(env_config: dict[str, str]) -> BaseUrl:
 def imap_client() -> Generator[Imbox, None, None]:
     """imap email client using credentials from environment variables"""
 
-    assert os.environ["IMAP_HOST"]
-    assert os.environ["IMAP_PORT"]
-    assert os.environ["IMAP_USER"]
-    assert os.environ["IMAP_PASS"]
+    assert os.environ["IMAP_HOST"], "required environment variable is undefined"
+    assert os.environ["IMAP_PORT"], "required environment variable is undefined"
+    assert os.environ["IMAP_USER"], "required environment variable is undefined"
+    assert os.environ["IMAP_PASS"], "required environment variable is undefined"
 
     imbox = Imbox(
         hostname=os.environ["IMAP_HOST"],