Fix test coverage to achieve 100% coverage on developing branch

tests/example_structure/project_summary.csv

@@ -1,16 +1,16 @@
 Name,Relative path,Description
-fine_mesh,data_cards\fine_mesh.tally,
-My transform,data_cards\my_transform.transform,
-Ring source,data_cards\ring_source.source,
-Main source,data_cards\volumetric_source.source,
-Wrong data card,data_cards\wrong_data_card.mat,
-Materials BAD,data_cards\materials_bad_library.mat,
-Standard materials,data_cards\materials.mat,
-Wrong suffix,data_cards\wrong_suffix.wrong,
-Model 1,models\filler_model_1.mcnp,
-Model 2,models\filler_model_2.mcnp,
-Envelope structure,models\main_input.mcnp,
-Model 3,models\path_to_be_excluded\filler_model_3.mcnp,
-Bad model 1,models\path_to_be_excluded\only_cells_block.mcnp,
-Bad model 2,models\path_to_be_excluded\wrong_surfaces_block.mcnp,
-Standard configuration,configurations\configuration_1.yml,
+fine_mesh,data_cards/fine_mesh.tally,
+My transform,data_cards/my_transform.transform,
+Ring source,data_cards/ring_source.source,
+Main source,data_cards/volumetric_source.source,
+Wrong data card,data_cards/wrong_data_card.mat,
+Materials BAD,data_cards/materials_bad_library.mat,
+Standard materials,data_cards/materials.mat,
+Wrong suffix,data_cards/wrong_suffix.wrong,
+Model 1,models/filler_model_1.mcnp,
+Model 2,models/filler_model_2.mcnp,
+Envelope structure,models/main_input.mcnp,
+Model 3,models/path_to_be_excluded/filler_model_3.mcnp,
+Bad model 1,models/path_to_be_excluded/only_cells_block.mcnp,
+Bad model 2,models/path_to_be_excluded/wrong_surfaces_block.mcnp,
+Standard configuration,configurations/configuration_1.yml,

tests/example_structure/project_summary_path_not_found.csv

@@ -1,2 +1,2 @@
 Name,Relative path,Description
-My file,data_cards\WRONG.tally,
+My file,data_cards/WRONG.tally,

tests/example_structure/project_summary_repeated_name.csv

@@ -1,3 +1,3 @@
 Name,Relative path,Description
-My file,data_cards\fine_mesh.tally,
-My file,data_cards\my_transform.transform,
+My file,data_cards/fine_mesh.tally,
+My file,data_cards/my_transform.transform,

tests/test_generate_model.py

@@ -1,8 +1,10 @@
 from pathlib import Path
+import tempfile
 
 import pytest
 
-from gitronics.generate_model import generate_model
+from gitronics.generate_model import generate_model, _get_envelope_structure_first_cell_id
+from gitronics.model_manager import ModelManager
 
 ROOT_FOLDER_PATH = Path(__file__).resolve().parents[1] / "tests" / "example_structure"
 PROJECT_SUMMARY_PATH = (
@@ -79,3 +81,41 @@ def test_envelope_name_not_found_in_envelope_structure(tmpdir):
             project_summary_path=PROJECT_SUMMARY_PATH,
             write_path=Path(tmpdir),
         )
+
+
+def test_get_envelope_structure_first_cell_id_no_digits():
+    """Test _get_envelope_structure_first_cell_id when no line starts with digits."""
+    # Create a temporary file with content that has no lines starting with digits
+    content = """C Comment line 1
+C Comment line 2
+C Another comment
+C No cell definitions
+C End of file"""
+
+    with tempfile.NamedTemporaryFile(mode='w', suffix='.mcnp', delete=False) as tmp_file:
+        tmp_file.write(content)
+        tmp_file.flush()
+
+        # Create a mock model manager with a project summary that points to our temp file
+        project_summary = {"test_envelope": Path(tmp_file.name)}
+
+        # Create a minimal configuration
+        class MockConfig:
+            envelope_structure = "test_envelope"
+
+        class MockModelManager:
+            def __init__(self):
+                self.project_summary = project_summary
+                self.configuration = MockConfig()
+
+        model_manager = MockModelManager()
+
+        # Test that the function raises ValueError when no cell ID is found
+        with pytest.raises(ValueError, match="Could not find the first cell ID"):
+            _get_envelope_structure_first_cell_id(model_manager)
+
+        # Clean up
+        Path(tmp_file.name).unlink()
+
+
+