Add test to ensure xml-model PI is excluded from output

Introduces a test verifying that xml-model processing instructions are not present in the output after pruning. Also updates macro search to use the _tag helper for consistency.

Author: adunning

tests/test_prune.py

@@ -1,4 +1,4 @@
-from style_variant_builder.prune import NS, CSLPruner
+from style_variant_builder.prune import CSLPruner, _tag
 
 EXAMPLE_XML = """<?xml version="1.0"?>
 <style xmlns="http://purl.org/net/xbiblio/csl">
@@ -12,6 +12,18 @@
 </style>
 """
 
+EXAMPLE_WITH_XML_MODEL = """<?xml version="1.0"?>
+<?xml-model href="http://example.com/schema.rng" type="application/xml"?>
+<style xmlns="http://purl.org/net/xbiblio/csl">
+  <macro name="test-macro"><text value="test"/></macro>
+  <citation>
+    <layout>
+      <text macro="test-macro"/>
+    </layout>
+  </citation>
+</style>
+"""
+
 
 def test_prune_removes_unused_macros(tmp_path):
     xml_path = tmp_path / "test.csl"
@@ -22,7 +34,7 @@ def test_prune_removes_unused_macros(tmp_path):
     pruner.build_used_macros()
     pruner.prune_macros()
     assert pruner.root is not None
-    macros = [m.get("name") for m in pruner.root.findall(f"{NS}macro")]
+    macros = [m.get("name") for m in pruner.root.findall(_tag("macro"))]
     assert "used-macro" in macros
     assert "unused-macro" not in macros
 
@@ -36,5 +48,24 @@ def test_prune_keeps_used_macros(tmp_path):
     pruner.build_used_macros()
     pruner.prune_macros()
     assert pruner.root is not None
-    macros = [m.get("name") for m in pruner.root.findall(f"{NS}macro")]
+    macros = [m.get("name") for m in pruner.root.findall(_tag("macro"))]
     assert "used-macro" in macros
+
+
+def test_xml_model_pi_excluded_from_output(tmp_path):
+    """Test that xml-model processing instructions are excluded from saved output."""
+    input_path = tmp_path / "input.csl"
+    output_path = tmp_path / "output.csl"
+    input_path.write_text(EXAMPLE_WITH_XML_MODEL)
+
+    pruner = CSLPruner(input_path, output_path)
+    pruner.parse_xml()
+    pruner.prune_macros()
+    pruner.save()
+
+    output_content = output_path.read_text()
+    # Verify xml-model PI is not in output
+    assert "<?xml-model" not in output_content
+    # Verify the actual content is preserved
+    assert "<macro" in output_content
+    assert "<citation>" in output_content