test-retest reliability using R programming

You are developing an instrument that measures vocational preferences (what people want to do for a living), and you need to administer the test several times during the year to students who are attending a vocational program. You need to assess the test-retest reliability of the test and the data from two administrations with Chapter 8 Data Set 2 (ch8ds2.csv) one in the fall and one in the spring. Would you call this a reliable test? Why or why not?