Add tests for writer models

java/ql/test/library-tests/dataflow/taint/JavaIo.java

@@ -0,0 +1,25 @@
+import java.io.*;
+
+public class JavaIo {
+  public static String taint() { return "tainted"; }
+  
+  public static void sink(Object o) { }
+
+  void testWritingChars() throws IOException {
+    StringWriter w = new StringWriter();
+    char[] chars = taint().toCharArray();
+    sink(w.toString());
+    w.write(chars);
+    sink(w.toString());
+    sink(w.getBuffer().toString());
+  }
+
+  void testAppendingToWriter() throws IOException {
+    StringWriter w = new StringWriter();
+    CharSequence seq = taint();
+    sink(w.toString());
+    w.append(seq);
+    sink(w.toString());
+  }
+
+}