CRUD application testing with mocha chai

I am new to JavaScript/JavaScript testing and was doing a course on mocha test framework with chai. how to test simple CRUD application? I want to write unit tests for all of them. I tried looking at questions here, but all of them were very advanced and i did not understand them. can you please help me it would be appreciated. the question was

module.exports = {
  
  addDetails: function() {
    let data =[]
    data.push("one");
    return data
  },

  deleteDetails: function() {
    let data =["one" , "two"]
    data.splice(0 , 1)
    return data
  },

  editDetails: function() {
    let data =["one"]
    data.splice(0 , 1 , "three")
    return data
  },

  updateDetails: function() {
    let data = ["one" , "three"]
    data.splice(1 , 0 , "two")
    return data
  },

  detailsPop: function() {
    let numb = ["one" , "two"]
    numb.pop()
    return numb
  },

  concatData: function() {
    let data1 = ["one"]
    let data2 = ["two"]
    let result = data1.concat(data2)
    return result
  }
 }