How do I write a unit test for a method which removes characters from a text file?

Question

I need to unit test a method which removes all the special characters like ,, : and some blank spaces.

The method under test stores each line of the file in a separate array position.

How do I test if the method removed all the special characters of a text file?

Answer 1

Write the file after your method call and use regex to ensure there are no special characters you don't want. Or compare file contents against a file that contains the result you wish to achieve.

Answer 2

The fakefs gem is good for this sort of thing.

In your spec setup (typically spec_helper.rb):

require 'fakefs/spec_helpers'

RSpec.configure do |config|
  config.treat_symbols_as_metadata_keys_with_true_values = true
  config.include FakeFS::SpecHelpers, fakefs: true
end

Here's the code under test. This function removes all punctuation:

require 'tempfile'

def remove_special_characters_from_file(path)
  contents = File.open(path, 'r', &:read)
  contents = contents.gsub(/\p{Punct}/, '')
  File.open(path, 'w') do |file|
    file.write contents
  end
end

And, finally, the spec:

require 'fileutils'

describe 'remove_special_characters_from_file', :fakefs do

  let(:path) {'/tmp/testfile'}

  before(:each) do
    FileUtils.mkdir_p(File.dirname(path))
    File.open(path, 'w') do |file|
      file.puts "Just a regular line."
    end
    remove_special_characters_from_file(path)
  end

  subject {File.open(path, 'r', &:read)}

  it 'should preserve non-puncuation' do
    expect(subject).to include 'Just a regular line'
  end

  it 'should not contain punctuation' do
    expect(subject).to_not include '.'
  end

end

Because we tagged this test's describe block with fakefs, no actual file system activity took place. The file system was fake, all in memory.