Simple instance_variable_set in RSpec does not work, but why not?

Question

I am kind of lost in a simple task in testing a Ruby app using RSpec:

class Script
  # content does not matter
  def initialize
  end

  def my_timezone_description(timeZoneId)
    @timeZonesCache[timeZoneId]
  end
end

Specs:

  it 'gets the timezone description' do
    Script.instance_variable_set(:@timeZonesCache, {123 => '+01:00'} )
    expect(Script.new.my_timezone_description(123)).to eq '+01:00'
  end

Script.instance_variable_get(:@timeZonesCache) gives me back the correct hash.

Can someone explain why this is not working and how I can get it to work?

Hint: instance_variable_set sets a variable on an instance. What instance are you calling it on? What instance are you reading the instance variable back from? — Jörg W Mittag
– Jörg W Mittag, Commented Nov 29, 2019 at 17:12

mrzasa · Accepted Answer · 2019-11-29 15:15:47Z

2

You need to call #instance_variable_set on Script instance, not on the class itself:

  it 'gets the timezone description' do
    script = Script.new
    script.instance_variable_set(:@timeZonesCache, ({123 => '+01:00'}) )
    expect(script.my_timezone_description(123)).to eq '+01:00'
  end

Otherwise you set instance variable for the class object, not for the instance object.

What you do now is a equivalent of

class Script
  @timeZonesCache = {123 => '+01:00'}
end

answered Nov 29, 2019 at 15:15

mrzasa

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