Incrementing an instance variable in the before :each clause of a MiniTest

Question

I'm writing a Ruby wrapper for a web-based API and each request requires a unique transaction ID to be sent along with the request.

I have written up a test shell using MiniTest::Spec, however the the transaction id is not incrementing between each test.

The test shell, leaving out tedious details, is as follows:

describe "should get the expected responses from the server" do
  before :all do
    # random number between 1 and maxint - 100
    @txid = 1 + SecureRandom.random_number(2 ** ([42].pack('i').size * 8 - 2) - 102)
    @username = SecureRandom.urlsafe_base64(20).downcase
  end

  before :each do
    # increment the txid
    @txid += 1
    puts "new txid is #{@txid}"
  end

  it "should blah blah" do
    # a test that uses @txid
  end

  it "should blah blah blah" do
    # a different test that uses the incremented @txid
  end
end

The puts line in there shows however that the @txid is not actually incrementing between each test.

A few more tests demonstrate that any assignment of a value to an instance variable within the body of a test has no effect on the value of the variable.

Is this expected? What is the correct way to handle this?

score 2 · Answer 1 · answered Sep 10 '13 at 20:19

Minitest runs each test in separate instances of the test class. Because of this instance variables are not shared between tests. To share values between tests you can use global or class variables.

describe "should get the expected responses from the server" do
  before do
    # random number between 1 and maxint - 100
    @@txid ||= SecureRandom.random_number(2 ** ([42].pack('i').size * 8 - 2) - 102)
    @@txid += 1 # increment the txid
    puts "new txid is #{@txid}"

    @@username ||= SecureRandom.urlsafe_base64(20).downcase
  end

  it "should blah blah" do
    # a test that uses @@txid
  end

  it "should blah blah blah" do
    # a different test that uses the incremented @@txid
  end
end

While possible this is probably not a good idea. :)

score 1 · Accepted Answer · edited May 23 '17 at 10:31

1

Minitest doesn't actually support before :all the way RSpec does. The type you pass into before do (such as :all or :each) is completely ignored in the underlying implementation.

See this issue for the relevant discussion, and note that the docs specify that: "type is ignored and is only there to make porting easier."

You could use class variables (not beautiful, but they'd meet your needs here). Alternatively, it looks like you can set up a custom runner if you use Minitest::Unit - check out the docs, this older answer, and this gist for more details.

edited May 23 '17 at 10:31

Community

1
1

answered Aug 13 '13 at 14:01

Danielle

158
4

Interesting. So before :all is in fact running before every test, not before all the tests. That's rather silly. But thanks for the pointers. – Dave Sag Aug 13 '13 at 23:10
Interestingly [this post](https://makandracards.com/makandra/11507-using-before-all-in-rspec-will-cause-you-lots-of-trouble-unless-you-know-what-you-are-doing) mades a good case for never using `before :all` in a test suite. – Dave Sag Aug 13 '13 at 23:16

Incrementing an instance variable in the before :each clause of a MiniTest

2 Answers2