There is a mistake in the description.
In the sentence:
Note: Make sure it works for a values other than 1.
it should rather be:
Note: Make sure it works for a values other than 0.
I think so, because for a = 0 we will not have a square function ;)

Ruby 3.0 should be enabled, see this to learn how to do it

Please organize the structure of test fixture as following (although it has been mentioned in the attached link, I'm repeated here again)

describe "<This message should describe the categories of test groups inside this block>" do
  it "<A short message describing this test group>" do
    expect(...).to eq(...) #Assertions
    #Or Test.assert_equals(user_response, reference_response)
  end
end

Are these overlapping or distinct squares?
Because 3x2 contains 2 overlapping 2x2 squares and 6 distinct 1x1 squares