Upgraded to a minimum of 5.4.0. It is now necessary * and will * not * work in the Minitest :: Test class, but assert * still works

The short answer is that as of 5.4.0 your test class must inherit from MiniTest :: Spec in order to use expectations.

I tested this on a new ubuntu machine with ruby ​​2.1.2 installed via RVM:

rvm install ruby-2.1.2

      

        
        
        
      

    

This code works with ruby ​​stock 2.1.2 (there is no set minimum of 5.4.0 minitest, slightly stripped down from your example code above):

#!/usr/bin/env ruby

require 'minitest/unit'
require "minitest/autorun"

class TestUserKey < MiniTest::Unit::TestCase

  def test_simple
    data = 0
    assert( data >= 0 )
    data.must_be :>=,0
  end

end

      

        
        
        
      

    

Running this code works fine. To reproduce the above error, install minitest 5.4.0:

gem install minitest -v 5.4.0

      

        
        
        
      

    

Now the code fails with the NoMethodError: undefined method `assert_operator 'for nil: NilClass". You now have both minitest versions:

~/.rvm/rubies/ruby-2.1.2/lib/ruby/2.1.0/minitest/  # stock ruby version of minitest
~/.rvm/gems/ruby-2.1.2/gems/minitest-5.4.0/        # minitest v5.4.0 installed via rubygems

      

        
        
        
      

    

Now that everything is set up, we can delve into what exactly is happening. Expectations are defined by calling infect_an_assertion, for example:

infect_an_assertion :assert_operator, :must_be, :reverse

      

        
        
        
      

    

For 5.4.0, this call happens in ~ / .rvm / gems / ruby-2.1.2 / gems / minitest-5.4.0 / lib / minitest / expect.rb. It's pretty much the same in both versions, it just happens elsewhere.

infect_an_assertion is also roughly the same for both versions. For: must_be this ends this call, which is identical between the two minitest versions:

MiniTest::Spec.current.#{meth}(args.first, self, *args[1..-1])

      

        
        
        
      

    

They do metaprogramming here, a runtime call will look more like this since meth is set to assert_operator:

MiniTest::Spec.current.assert_operator(...)

      

        
        
        
      

    

The important part is MiniTest :: Spec.current. In 5.4.0, this method returns nil, which results in a NoMethodError exception when it tries to call assert_operator to nil.

In stock minitest from ruby ​​2.1.2:

Here MiniTest :: Spec inherits from MiniTest :: Unit :: TestCase. TestCase defines a current method and returns the value that was set in the initialize method. You can see this is all happening around line 1303 ~ / .rvm / rubies / ruby-2.1.2 / lib / ruby ​​/2.1.0/minitest/unit.rb:

def initialize name # :nodoc:
  @__name__ = name
  @__io__ = nil
  @passed = nil
  @@current = self # FIX: make thread local
end

def self.current # :nodoc:
  @@current # FIX: make thread local
end

      

        
        
        
      

    

Therefore, when you inherit MiniTest :: Unit :: TestCase in your test class with minimal margin, the current one is defined as a method and is guaranteed to return a value when the above MiniTest :: Spec.current call is made. This is why it works in the ruby ​​stock 2.1.2 minitest.

In minitest 5.4.0

In 5.4.0 Minitest :: Spec inherits from Minitest :: Test, which does not define current (and neither of its parents). The current method is defined directly in Minitest :: Spec. It just returns Thread.current [: current_spec]:

# line 83 of ~/.rvm/gems/ruby-2.1.2/gems/minitest-5.4.0/lib/minitest/spec.rb      
def self.current # :nodoc:
  Thread.current[:current_spec]
end

      

        
        
        
      

    

The Thread.current [: current_spec] value is set in the Minitest :: Spec constructor on line 87 of the same file:

def initialize name # :nodoc:
  super
  Thread.current[:current_spec] = self
end

      

        
        
        
      

    

The problem is that when your test class inherits from Minitest :: Test, the Minitest :: Spec constructor is never called, and Thread.current [: current_spec] is never initialized. This means that the call to infect_an_assertion in Minitest :: Spec.current returns nil, which results in the NoMethodError you see when it tries to call assert_operator on nil. The solution is to make your test class inherit from Minitest :: Spec so that the constructor is called and Thread.current [: current_spec] gets the value.

Here's a slightly modified version of the source that works with minitest 5.4.0:

#!/usr/bin/env ruby

gem 'minitest'
require "minitest/autorun"

class TestUserKey < Minitest::Spec

  def test_simple
    data = 0
    assert( data >= 0 )
    data.must_be :>=,0
  end

end

      

        
        
        
      

    

Hope this helps!