Trouble subtracting dates in JS

Question

I'm running this code in my vue component from a datepicker which returns the dates as shown in my data below.

Everything is good, except for when I console.log the days variable it's 0 when it should definitely be a larger number

Am I converting it incorrectly?

var vm = 
new Vue({
  el: "#app",
  data: {
    date_test1:'2021-02-02',
    date_test2:'2021-05-15'
  },
  methods: {
    
    testDate(){
      
      const diff_in_days = Math.abs(new Date(date_test1) - new Date(date_test2));
      
      const days = Math.ceil(diff_in_days / (1000 * 60 * 60 * 24));

      console.log(days);
    }
  }
  
  });

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