ruby on rails - RSpec throws a NoMethodError, but method works in the app -

i have method 'current_balance' defined in invoice.rb:

class invoice < activerecord::base   belongs_to :purchase   has_many :payments, dependent: :destroy    validates :number, presence: true   validates :currency, format: {with: /\a[a-z]+\z/, message: "please enter 3 letter currency code in caps."}   validates :total_due, presence: true   validates :due_date, format: {with: /\d{4}-\d{2}-\d{2}/, message: "format must yyyy-mm-dd"}   validates :status, presence: true    def self.next_due     where("due_date >= ? , status = ?", time.now, 'open').order("due_date desc").first ? where("due_date >= ?", time.now).order("due_date desc").first.due_date : ''   end    def self.overdue     where("due_date < ? , status = ?", time.now, 'open').order("due_date desc").first ? where("due_date < ?", time.now).order("due_date desc").first.due_date : ''   end    def current_balance     self.current_balance = (self.total_due - self.payments.sum(:amount_paid))   end    def status     if self.current_balance > 0       self.status = "open"     elsif self.current_balance < 0       self.status = "overpaid"     elsif self.current_balance = 0       self.status = "paid"     end   end end 

the factory, invoices.rb

factorygirl.define   factory :invoice     sequence(:id) { |number| number }     sequence(:purchase_id) { |n| n }     number { ffaker::string.from_regexp(/\a[a-za-z0-9]+\z/) }     terms { ffaker::string.from_regexp(/\a[a-za-z0-9\s]+\z/) }     currency { ffaker::string.from_regexp(/\a[a-z]+\z/) }     total_due {'200.00'}     due_date { ffaker::time.date }     notes { ffaker::hipsteripsum.paragraph }     status {[:open, :paid, :canceled].sample}   end    factory :invalid_invoice, parent: :invoice     currency nil   end end 

the model spec, invoices_spec.rb contains:

require "spec_helper"  describe invoice, '#current_balance'   "calculates current balance of invoice"     invoice = factorygirl.create(:invoice, total_due: 200)     invoice.payments << factorygirl.create(:payment, amount_paid: 100)     invoice.payments << factorygirl.create(:payment, amount_paid: 50)     expect(invoice.current_balance).to eq(50)   end end  describe invoice   before(:all) { @invoice = factorygirl.build(:invoice) }     "has valid factory"       expect(factorygirl.create(:invoice)).to be_valid     end      "is invalid without number"       invoice = invoice.new(number: nil)       expect(invoice).to_not be_valid     end      "is invalid without currency"       invoice = invoice.new(currency: nil)       expect(invoice).to_not be_valid     end      "is invalid without total_due"       invoice = invoice.new(total_due: nil)       expect(invoice).to_not be_valid     end      "is invalid without due_date"       invoice = invoice.new(due_date: nil)       expect(invoice).to_not be_valid     end      "is invalid without status"       invoice = invoice.new(status: nil)       expect(invoice).to_not be_valid     end  end 

the method works , calculates current balance of invoice when run app. when run model spec, however, error.

the '#current_balance' & 'it has valid factory' examples pass, rest fail same error.

failure/error: expect(invoice).to_not be_valid nomethoderror:  undefined method `-' nil:nilclass 

what doing wrong?

ah, full model code problem crystal clear. starts line:

validates :status, presence: true 

it triggers getter of status, triggers getter of current_balance sets self.current_balance subtracting total_due not set (is nil) in of failing test cases. hence error message.