Distribute edge case tests into appropriate test files

Move tests from standalone test_coverage_improvements.py into existing
test files where they belong:

- test_flu.py: 52 edge case tests added inline to existing test functions
  - Empty iterator handling (reduce, min, max, sum, count)
  - Attribute/item access errors (map_item, map_attr)
  - Parameter edge cases (head/tail/take with 0, collect with 0)
  - __getitem__ edge cases (negative index, slices with step)
  - Side effect exception handling
  - Integration tests for complex pipelines

- test_cli.py: 4 error handling tests
  - Non-existent module import
  - Non-existent attribute import
  - Empty import list
  - Exception propagation from commands

- test_cli_utils.py: 4 utility edge case tests
  - Return type verification
  - Empty directory handling

Removed standalone coverage files in favor of inline tests.

Author: claude

TEST_COVERAGE_ANALYSIS.md

@@ -109,3 +109,30 @@ def test_glob_imports(capsys):
     result = capsys.readouterr()
     stdout = result.out
     assert stdout
+
+
+# Error handling tests
+
+
+def test_import_nonexistent_module_raises():
+    """Importing non-existent module should raise ModuleNotFoundError."""
+    with pytest.raises(ModuleNotFoundError):
+        build_import_dict(["nonexistent_module_xyz123"])
+
+
+def test_import_nonexistent_attribute_raises():
+    """Importing non-existent attribute should raise AttributeError."""
+    with pytest.raises(AttributeError):
+        build_import_dict(["json:nonexistent_function"])
+
+
+def test_build_import_dict_empty_list():
+    """build_import_dict with empty list should return empty dict."""
+    result = build_import_dict([])
+    assert result == {}
+
+
+def test_cli_exception_in_command():
+    """CLI should propagate exceptions from user commands."""
+    with pytest.raises(ZeroDivisionError):
+        main(["flu", "1/0"])

src/tests/test_cli.py

@@ -1,3 +1,4 @@
+from flupy import flu
 from flupy.cli.utils import walk_dirs, walk_files
 
 
@@ -8,3 +9,36 @@ def test_walk_files():
 
 def test_walk_dirs():
     assert walk_dirs().head()
+
+
+# Edge case tests
+
+
+def test_walk_files_returns_fluent():
+    """walk_files() should return a Fluent object."""
+    result = walk_files()
+    assert isinstance(result, flu)
+
+
+def test_walk_dirs_returns_fluent():
+    """walk_dirs() should return a Fluent object."""
+    result = walk_dirs()
+    assert isinstance(result, flu)
+
+
+def test_walk_files_empty_directory(tmp_path):
+    """walk_files() on empty directory should return empty."""
+    empty_dir = tmp_path / "empty"
+    empty_dir.mkdir()
+    result = walk_files(str(empty_dir)).collect()
+    assert result == []
+
+
+def test_walk_dirs_empty_directory(tmp_path):
+    """walk_dirs() on directory with no subdirs returns root only."""
+    empty_dir = tmp_path / "empty"
+    empty_dir.mkdir()
+    result = walk_dirs(str(empty_dir)).collect()
+    # walk_dirs includes the root directory itself
+    assert len(result) == 1
+    assert str(empty_dir) in result[0]