Java: add test case

java/ql/test/library-tests/dataflow/implicit-read/A.java

@@ -0,0 +1,27 @@
+public class A {
+    String field;
+
+    static String source(String name) {
+        return name;
+    }
+
+    static void sink(Object o) {}
+
+    static String step(Object o) {
+        return "";
+    }
+
+    static Object getA() {
+        A a = new A();
+        a.field = source("source");
+        return a;
+    }
+
+    static void test() {
+        Object object = getA();
+
+        sink(step(object)); // $ hasTaintFlow=source
+        sink(object); // $ SPURIOUS: hasTaintFlow=source
+        sink(((A)object).field); // $ hasTaintFlow=source
+    }
+}