diff --git a/src/test/java/org/apache/commons/xml/secure/SaxonTransformerExternalCallsTest.java b/src/test/java/org/apache/commons/xml/secure/SaxonTransformerExternalCallsTest.java
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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.commons.xml.secure;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.StringWriter;
+
+import javax.xml.transform.TransformerException;
+import javax.xml.transform.TransformerFactory;
+import javax.xml.transform.stream.StreamResult;
+
+import org.junit.jupiter.api.Assumptions;
+import org.junit.jupiter.api.Tag;
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests whether Saxon's XSLT 3.0 URI-fetching functions can pull external resources into a transform result through a secure {@code TransformerFactory}.
+ *
+ * <p>The XPath 3.1 {@code unparsed-text} family and {@code json-doc} do not go through the JAXP {@code URIResolver} that governs {@code document()} and
+ * {@code xsl:include}/{@code xsl:import}: Saxon routes them through the {@code Configuration}'s resource resolver. This test is the TrAX-side companion of
+ * {@link SaxonXPathExternalCallsTest}, confirming that the floor {@code SaxonProvider} installs on the transformer path also closes these functions when they
+ * are called from a stylesheet.</p>
+ *
+ * <p>The three content functions ({@code unparsed-text}, {@code unparsed-text-lines}, {@code json-doc}) are checked as a leak pair: an unconfigured Saxon
+ * factory resolves the URI and copies {@link AttackTestSupport#LEAKED_MARKER} into the output, while the secure factory must not. {@code unparsed-text-available}
+ * discloses no content, so it is checked as an existence oracle: the unconfigured factory distinguishes an existing fixture from a missing one, and the secure
+ * factory must not.</p>
+ *
+ * <p>Saxon is instantiated reflectively and every test skips when it is absent, so under the surefire group filters the checks are effective on the test-saxon
+ * and test-saxon-xerces executions.</p>
+ */
+@Tag("trax")
+class SaxonTransformerExternalCallsTest {
+
+    private static final String SAXON_TRANSFORMER_FACTORY_CLASS = "net.sf.saxon.TransformerFactoryImpl";
+
+    private static void assumeSaxonPresent() {
+        boolean present;
+        try {
+            Class.forName(SAXON_TRANSFORMER_FACTORY_CLASS);
+            present = true;
+        } catch (final ClassNotFoundException e) {
+            present = false;
+        }
+        Assumptions.assumeTrue(present, "Saxon is not on the classpath");
+    }
+
+    /** Wraps a single XPath 3.1 expression in an XSLT 3.0 stylesheet that copies its string value into the output. */
+    private static String stylesheet(final String expression) {
+        return "<?xml version=\"1.0\"?>\n"
+                + "<xsl:stylesheet version=\"3.0\" xmlns:xsl=\"http://www.w3.org/1999/XSL/Transform\">\n"
+                + "  <xsl:template match=\"/\">\n"
+                + "    <leaked><xsl:value-of select=\"" + expression + "\"/></leaked>\n"
+                + "  </xsl:template>\n"
+                + "</xsl:stylesheet>\n";
+    }
+
+    /** URL of a fixture that carries {@link AttackTestSupport#LEAKED_MARKER}; {@code name} is a file under {@code src/test/resources/leaked/}. */
+    private static String url(final String name) {
+        return AttackTestSupport.resourceUrl(name).toString();
+    }
+
+    /** URL of a sibling resource that does not exist, so a real fetch fails; used as the negative side of the existence-oracle check. */
+    private static String missingUrl() {
+        return url("referenced.txt").replaceFirst("referenced\\.txt$", "does-not-exist.txt");
+    }
+
+    private static TransformerFactory saxonFactory() {
+        try {
+            return (TransformerFactory) Class.forName(SAXON_TRANSFORMER_FACTORY_CLASS).getDeclaredConstructor().newInstance();
+        } catch (final ReflectiveOperationException e) {
+            throw new AssertionError("Cannot instantiate " + SAXON_TRANSFORMER_FACTORY_CLASS, e);
+        }
+    }
+
+    private static String transform(final TransformerFactory factory, final String expression) throws TransformerException {
+        final StringWriter sink = new StringWriter();
+        factory.newTemplates(AttackTestSupport.streamSource(stylesheet(expression))).newTransformer()
+                .transform(AttackTestSupport.streamSource("<root/>"), new StreamResult(sink));
+        return sink.toString();
+    }
+
+    /** Runs the expression through the secure Saxon factory; a throw is an acceptable block, otherwise the marker must be absent. */
+    private static void assertSecureDoesNotLeak(final String expression) {
+        try {
+            final String result = transform(SecureTransformerFactory.secure(saxonFactory()), expression);
+            assertFalse(result.contains(AttackTestSupport.LEAKED_MARKER), "secure Saxon transform leaked through " + expression + ":\n" + result);
+        } catch (final TransformerException blocked) {
+            // Throwing also prevents the leak.
+        }
+    }
+
+    /** Runs the expression through the unconfigured Saxon factory and asserts the marker is resolved into the output (leak control). */
+    private static void assertUnconfiguredLeaks(final String expression) throws TransformerException {
+        final String result = transform(saxonFactory(), expression);
+        assertTrue(result.contains(AttackTestSupport.LEAKED_MARKER), "unconfigured Saxon was expected to resolve " + expression + ", got: " + result);
+    }
+
+    @Test
+    void secureTransformerBlocksUnparsedText() {
+        assumeSaxonPresent();
+        assertSecureDoesNotLeak("unparsed-text('" + url("referenced.txt") + "')");
+    }
+
+    @Test
+    void secureTransformerBlocksUnparsedTextLines() {
+        assumeSaxonPresent();
+        assertSecureDoesNotLeak("string-join(unparsed-text-lines('" + url("referenced.txt") + "'), ' ')");
+    }
+
+    @Test
+    void secureTransformerBlocksJsonDoc() {
+        assumeSaxonPresent();
+        assertSecureDoesNotLeak("json-doc('" + url("referenced.json") + "')?leaked");
+    }
+
+    @Test
+    void secureTransformerHidesUnparsedTextAvailability() {
+        assumeSaxonPresent();
+        // The unconfigured factory is a working existence oracle: true for the fixture, false for a missing sibling.
+        final TransformerFactory unconfigured = saxonFactory();
+        try {
+            assertTrue(transform(unconfigured, "unparsed-text-available('" + url("referenced.txt") + "')").contains("true"),
+                    "unconfigured Saxon should report the fixture as available");
+            assertTrue(transform(unconfigured, "unparsed-text-available('" + missingUrl() + "')").contains("false"),
+                    "unconfigured Saxon should report the missing sibling as unavailable");
+        } catch (final TransformerException e) {
+            throw new AssertionError("unconfigured Saxon unparsed-text-available control failed", e);
+        }
+        // The secure factory must not reflect the real filesystem: the answer for the fixture and the missing sibling must match, so it is no oracle.
+        final String secureExisting = availabilityUnderSecure(url("referenced.txt"));
+        final String secureMissing = availabilityUnderSecure(missingUrl());
+        assertNotEquals("true:false", secureExisting + ":" + secureMissing,
+                "secure Saxon unparsed-text-available still distinguishes an existing file from a missing one");
+    }
+
+    /** The {@code unparsed-text-available} answer under the secure factory, or {@code "blocked"} when the transform throws. */
+    private static String availabilityUnderSecure(final String uri) {
+        try {
+            return transform(SecureTransformerFactory.secure(saxonFactory()), "unparsed-text-available('" + uri + "')").contains("true") ? "true" : "false";
+        } catch (final TransformerException blocked) {
+            return "blocked";
+        }
+    }
+
+    @Test
+    void unconfiguredTransformerLeaksUnparsedText() throws TransformerException {
+        assumeSaxonPresent();
+        assertUnconfiguredLeaks("unparsed-text('" + url("referenced.txt") + "')");
+    }
+
+    @Test
+    void unconfiguredTransformerLeaksUnparsedTextLines() throws TransformerException {
+        assumeSaxonPresent();
+        assertUnconfiguredLeaks("string-join(unparsed-text-lines('" + url("referenced.txt") + "'), ' ')");
+    }
+
+    @Test
+    void unconfiguredTransformerLeaksJsonDoc() throws TransformerException {
+        assumeSaxonPresent();
+        assertUnconfiguredLeaks("json-doc('" + url("referenced.json") + "')?leaked");
+    }
+}