add unit tests for input and output path validation functions

tests/unit/test_file_ops.py

@@ -1,6 +1,10 @@
 from pathlib import Path
 
-from concatenator.file_ops import add_label_to_path
+import pytest
+
+from concatenator.file_ops import add_label_to_path, validate_input_path, validate_output_path
+
+from .. import data_for_tests_dir
 
 
 def test_add_label_to_path():
@@ -10,3 +14,27 @@ def test_add_label_to_path():
     new_path = str((this_module_dir / "tests_file_new-suffix.nc").resolve())
 
     assert add_label_to_path(origin_path, label="_new-suffix") == new_path
+
+
+def test_validate_bad_output_paths():
+    path_to_file_that_exists = str(
+        data_for_tests_dir / "unit-test-data" / "TEMPO_NO2_L2_V03_20240328T154353Z_S008G01.nc4"
+    )
+
+    with pytest.raises(FileExistsError):
+        validate_output_path(path_to_file_that_exists, overwrite=False)
+
+    with pytest.raises(TypeError):
+        validate_output_path(str(data_for_tests_dir), overwrite=False)
+
+
+def test_validate_bad_non_existent_input_path():
+    path_to_file_that_does_not_exist = str(
+        data_for_tests_dir / "unit-test-data" / "non-existent.nc4"
+    )
+
+    with pytest.raises(TypeError):
+        validate_input_path([path_to_file_that_does_not_exist])
+
+    with pytest.raises(TypeError):
+        validate_input_path([])