stop tests from checking error messages - we should be using the name, not fragile checks

Author: bitplane

CLAUDE.md

@@ -12,11 +12,11 @@ The project follows a layered architecture:
 
 1. **Main Entry Point** (`main.py`): CLI interface that manages device monitoring and server lifecycle
 2. **Server Layer** (`server.py`): Orchestrates nbdkit, nbdfuse, and FUSE mounting
-3. **Plugin Layer** (`plugin.py`): nbdkit Python plugin that handles block device operations
-4. **Cache Layer** (`cache/`): Abstract caching interface and implementations
-5. **DiskMap** (`diskmap.py`): ddrescue-compatible mapfile handling for tracking read status
+3. **Backend Layer** (`backend.py`): nbdkit Python plugin that handles block device operations
+4. **File Layer** (`file/`): Modular file abstraction with automatic type detection and composition
+5. **FileMap** (`file/filemap.py`): ddrescue-compatible mapfile handling for tracking read status
 
-The cache implementation appears to be in transition from a legacy global state approach to a more modular `Cache` class architecture.
+The implementation is in transition from a legacy global state approach in the backend to a modular File-based architecture using composition over inheritance.
 
 ## Development Commands
 
@@ -58,7 +58,7 @@ Tests use pytest (functional style, not unittest OOP style). Test files mirror t
 2. **Block Size**: Default is 4KB, but can be auto-detected based on device type or specified manually
 3. **Caching**: Uses memory-mapped files for sector caching
 4. **Disk Status Tracking**: Compatible with ddrescue format for tracking read status
-5. **Transitions**: The DiskMap uses a transition-based approach for efficiently representing block states
+5. **Transitions**: The FileMap uses a transition-based approach for efficiently representing block states
 
 ## Code Style
 

tests/unit/file/test_filemap.py

@@ -267,13 +267,13 @@ def test_set_status_invalid_input(filemap):
 
 def test_slice_bounds_negative_start(filemap):
     """Test that negative start indices raise ValueError."""
-    with pytest.raises(ValueError, match="Negative start index"):
+    with pytest.raises(ValueError):
         filemap[-1:50] = STATUS_OK
 
 
 def test_slice_bounds_stop_beyond_size(filemap):
     """Test that stop indices beyond device size raise ValueError."""
-    with pytest.raises(ValueError, match="Stop index beyond device size"):
+    with pytest.raises(ValueError):
         filemap[0:101] = STATUS_OK
 
 
@@ -373,11 +373,11 @@ def test_getitem_slice_empty_range(filemap):
 def test_getitem_slice_bounds_checking(filemap):
     """Test __getitem__ slice bounds checking."""
     # Negative start should raise error
-    with pytest.raises(ValueError, match="Negative start index"):
+    with pytest.raises(ValueError):
         filemap[-1:50]
 
     # Stop beyond size should raise error
-    with pytest.raises(ValueError, match="Stop index beyond device size"):
+    with pytest.raises(ValueError):
         filemap[0:101]
 
 
@@ -456,7 +456,7 @@ def test_pos_property_corrupted_no_untried(filemap):
     """Test pos property raises error when transitions are corrupted."""
     filemap.transitions = [(0, NO_SORT, STATUS_OK), (100, NO_SORT, STATUS_OK)]  # No untried
 
-    with pytest.raises(ValueError, match="FileMap transitions corrupted, someone deleted the end one"):
+    with pytest.raises(ValueError):
         filemap.pos
 
 
@@ -492,7 +492,7 @@ def test_status_property_corrupted_insufficient_transitions():
     filemap = FileMap(100)
     filemap.transitions = [(0, NO_SORT, STATUS_OK)]  # Missing end marker
 
-    with pytest.raises(ValueError, match="insufficient entries"):
+    with pytest.raises(ValueError):
         filemap.status
 
 
@@ -502,7 +502,7 @@ def test_status_property_corrupted_no_valid_statuses():
     # Corrupt the transitions to have invalid status
     filemap.transitions = [(0, NO_SORT, "INVALID"), (100, NO_SORT, "INVALID")]
 
-    with pytest.raises(ValueError, match="no valid statuses found"):
+    with pytest.raises(ValueError):
         filemap.status