private String generateExecutionPlan(String filter, String fields) {
        return new StringBuilder()
                .append("@App:name('filterTest1') ")
                .append("define stream cseEventStream (").append(fields).append(");")
                .append("@info(name = 'query1') ")
                .append("from cseEventStream[").append(filter).append("] ")
                .append("select symbol, price ")
                .append("insert into outputStream;")
                .toString();
    }
Test expression comparisons with String values.
modules/siddhi-core/src/test/java/io/siddhi/core/query/StringCompareTestCase.java