Java: add single-method class test case for mocking rule

Classes with only one public method should be compliant when mocked.

java/ql/test/query-tests/MockingAllNonPrivateMethodsMeansUnitTestIsTooBig/EmployeeStatus.java

@@ -0,0 +1,9 @@
+/**
+ * Simple class with a single public method to test the edge case.
+ * When this single method is mocked, it means ALL public methods are mocked.
+ */
+public class EmployeeStatus {
+    public String getStatus() {
+        return "active";
+    }
+}