Added validation for the time_format option and wrote tests for it

tests/test_create_filenames.py

@@ -1,10 +1,11 @@
 import pytest
 from tibi_hardlinks.filename_creation import create_backup_directory_name
+from tibi_hardlinks.exceptions import ConfigurationException
 
 
 @pytest.mark.usefixtures("canned_data_output")
 @pytest.mark.parametrize("filename", ["example-old", "example-new"])
-def test_filename_good(filename, canned_data_output):
+def test_filename_good_canned(filename, canned_data_output):
     data = canned_data_output(filename)
     filenames = {
         "example-old": "XT1095/TA44909SO3/QPython3/1.0.3/2017-11-01_07-38-42",
@@ -13,3 +14,16 @@ def test_filename_good(filename, canned_data_output):
 
     generated_filename = create_backup_directory_name(data)
     assert filenames[filename] == generated_filename
+
+
+def test_filename_raise_on_bad_time_format(canned_data_output):
+    data = canned_data_output("example-new")
+
+    with pytest.raises(ConfigurationException):
+        create_backup_directory_name(data, "obviously bogus time format")
+
+
+def test_filename_raise_on_incomplete_exception(canned_data_output):
+    data = canned_data_output("example-new")
+    with pytest.raises(ConfigurationException):
+        create_backup_directory_name(data, "%Y-%M-%D")

tibi_hardlinks/exceptions.py

@@ -0,0 +1,7 @@
+class ConfigurationException(Exception):
+    def __init__(self, section, key, value):
+        self.section = section
+        self.key = key
+        self.value = value
+        self.message = f"Invalid value for {self.section}:{self.key}='{self.value}'"
+        super().__init__(self.message)

tibi_hardlinks/filename_creation.py

@@ -1,6 +1,9 @@
 import datetime
 import os
 
+
+from tibi_hardlinks.exceptions import ConfigurationException
+
 HEIRACHY = (
     "sys_ro.product.model",
     "sys_ro.serialno",
@@ -13,7 +16,13 @@ HEIRACHY = (
 def create_backup_directory_name(backup_info, time_format="%Y-%m-%d_%H-%M-%S"):
     utc_timestamp = backup_info["backup_time"]
     backup_datetime = datetime.datetime.utcfromtimestamp(utc_timestamp)
-    backup_info["backup_time"] = backup_datetime.strftime(time_format)
+
+    try:
+        new_time = backup_datetime.strftime(time_format)
+        assert backup_datetime == datetime.datetime.strptime(new_time, time_format)
+        backup_info["backup_time"] = new_time
+    except (ValueError, AssertionError):
+        raise ConfigurationException("customization", "time_format", time_format)
     ret_list = []
     for part in HEIRACHY:
         data = backup_info[part]