Test coverage for PatchedXMLWriter (#405)

Co-authored-by: Björn Ekryd <bjornatekryd.se>

sorter/src/test/java/sortpom/output/PatchedXMLWriterTest.java

@@ -0,0 +1,40 @@
+package sortpom.output;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.io.StringReader;
+import java.io.StringWriter;
+import org.dom4j.io.OutputFormat;
+import org.dom4j.io.SAXReader;
+import org.junit.jupiter.api.Test;
+
+class PatchedXMLWriterTest {
+
+  /** Copied, with gratitude, from Dom4J */
+  @Test
+  public void writeXmlWithDocType() throws Exception {
+    var xml =
+        "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n"
+            + "<!DOCTYPE xml [\n"
+            + "  <!ENTITY copy \"©\">\n"
+            + "  <!ENTITY trade \"™\">\n"
+            + "  <!ENTITY deg \"°\">\n"
+            + "  <!ENTITY gt \"&#62;\">\n"
+            + "  <!ENTITY sup2 \"²\">\n"
+            + "  <!ENTITY frac14 \"¼\">\n"
+            + "  <!ENTITY quot \"&#34;\">\n"
+            + "  <!ENTITY frac12 \"½\">\n"
+            + "  <!ENTITY euro \"€\">\n"
+            + "  <!ENTITY Omega \"Ω\">\n"
+            + "]><root/>";
+
+    var reader = new SAXReader();
+    reader.setIncludeInternalDTDDeclarations(true);
+
+    var wr = new StringWriter();
+    var writer = new PatchedXMLWriter(wr, new OutputFormat(), false, false, false, false);
+    writer.write(reader.read(new StringReader(xml)));
+
+    assertEquals(xml, wr.toString());
+  }
+}