private stub

x.rb

require 'rspec/autorun'

class X
  def call
    fund_query
  end

  private

  def fund_qeuery
    raise 'DB acces'
  end
end

RSpec.describe X do
  let(:x) { X.new }

  before do
    # allow(x).to receive(:foo).and_call_original
    allow(x).to receive(:fund_query).and_return(13)
  end

  it 'is 13' do
    expect(x.call).to eq 13
  end
end

# >> 
# >> Randomized with seed 49010
# >> .
# >> 
# >> Top 1 slowest examples (0.00634 seconds, 52.3% of total time):
# >>   X is 13
# >>     0.00634 seconds /var/folders/6h/wj2by4nn7716wzgzgdbh7twmt3k49g/T/seeing_is_believing_temp_dir20200127-89638-1byy5jg/program.rb:23
# >> 
# >> Finished in 0.01212 seconds (files took 0.12542 seconds to load)
# >> 1 example, 0 failures
# >> 
# >> Randomized with seed 49010
# >>