Refactor for easier unit testing and add unit tests

tests/unit/test_editor.py

@@ -0,0 +1,41 @@
+# Copyright © 2012-2023 jrnl contributors
+# License: https://www.gnu.org/licenses/gpl-3.0.html
+
+import pathlib
+from unittest.mock import mock_open
+from unittest.mock import patch
+
+import pytest
+
+from jrnl.editor import get_template_path
+from jrnl.editor import read_template_file
+from jrnl.exception import JrnlException
+
+
+@patch("builtins.open", side_effect=FileNotFoundError())
+def test_read_template_file_with_no_file_raises_exception(mock_open):
+    with pytest.raises(JrnlException) as ex:
+        read_template_file("invalid_file.txt")
+        assert isinstance(ex.value, JrnlException)
+
+
+@patch("builtins.open", new_callable=mock_open, read_data="template text")
+def test_read_template_file_with_valid_file_returns_text(mock_file):
+    assert read_template_file("valid_file.txt") == "template text"
+
+
+def test_get_template_path_when_exists_returns_correct_path():
+    template_path = pathlib.Path("templatepath")
+
+    with patch.object(pathlib.Path, "exists", lambda _: True):
+        output = get_template_path("template", template_path)
+
+    assert output == str(template_path / "template")
+
+
+@patch("jrnl.editor.absolute_path")
+def test_get_template_path_when_doesnt_exist_returns_correct_path(mock_absolute_paths):
+    with patch.object(pathlib.Path, "exists", lambda _: False):
+        output = get_template_path("template", pathlib.Path("templatepath"))
+
+    assert output == str(mock_absolute_paths.return_value)