[RAILS] How to override in a model unit test so that Faker can be used to generate random values


I thought Faker could only be used with FactoryBot, but I realized that RSpec can also be used with files that describe unit test code for models, and I'll record what I've learned anew.


A description that randomly generates numbers.

As a basic usage,

Faker::Number.between(from: 5, to: 11) #Randomly generate 5 or more and 11 or less

You can also reduce the conditions.

Faker::Number.between(from: 11) #Randomly generate 11 or more

It says between, but if you don't addto:, you can generate a value without setting a maximum value. vice versa,

Faker::Number.between(to: 11) #Randomly generate 11 or less

If you change from: to to:, you can generate a value with only the highest value.

Specific usage


It is a code to confirm whether 8 or more cannot be entered in the field for entering the grade.

Test code

before do
  @class_room = FactoryBot.build(:class_room)
it 'Cannot register if the grade is 8 or above' do
  @class_room.grade = Faker::Number.between(from: 8) #Overwrite the part you want to check
  expect(@class_room.errors.full_messages).to include("The grade is not on the list")


Since Rails makes it convenient to use Ruby, I just notice every day that there are many "why" black boxes. In this case, I assumed that Faker was only in FactoryBot.

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