diff --git a/tests/notifications-python-client/test_utils.py b/tests/notifications-python-client/test_utils.py
new file mode 100644
index 000000000..6363e2884
--- /dev/null
+++ b/tests/notifications-python-client/test_utils.py
@@ -0,0 +1,37 @@
+import base64
+from io import BytesIO
+
+from notifications_python_client.utils import DOCUMENT_UPLOAD_SIZE_LIMIT, prepare_upload
+
+
+def test_prepare_upload_success():
+    content = b"hello world"
+    f = BytesIO(content)
+    filename = "test.txt"
+    confirm_email_before_download = True
+    retention_period = "1 day"
+
+    result = prepare_upload(
+        f,
+        filename=filename,
+        confirm_email_before_download=confirm_email_before_download,
+        retention_period=retention_period,
+    )
+    expected = {
+        "file": base64.b64encode(content).decode("ascii"),
+        "filename": filename,
+        "confirm_email_before_download": confirm_email_before_download,
+        "retention_period": retention_period,
+    }
+    assert result == expected
+
+
+def test_prepare_upload_file_too_large():
+    content = b"a" * (DOCUMENT_UPLOAD_SIZE_LIMIT + 1)
+    f = BytesIO(content)
+
+    try:
+        prepare_upload(f)
+        assert 1 == 0, "Expected ValueError for large file"
+    except ValueError as e:
+        assert str(e) == "File is larger than 2MB"