Java: Add test case for StringEscapeUtils.escapeJson() taint step.

Author: Sebastian Bauersfeld

java/ql/test/library-tests/frameworks/apache-commons-lang3/StringEscapeUtilsTest.java

@@ -0,0 +1,11 @@
+import org.apache.commons.lang3.StringEscapeUtils;
+
+public class StringEscapeUtilsTest {
+  String taint() { return "tainted"; }
+
+  void sink(Object o) {}
+
+  void test() throws Exception {
+    sink(StringEscapeUtils.escapeJson(taint())); // $hasTaintFlow
+  }
+}