The word its

Many contexts hold one method and one expectation:

require "fix"

Fix :Team do
  on :size do
    it MUST eq 3
  end

  on :first do
    it MUST eq "Ada"
  end
end

exit(Fix[:Team].test { %w[Ada Grace Linus] })

With fix-its, each of them takes one line. Install it, gem install fix-its or gem "fix-its" in a Gemfile, and require fix/its, which requires fix:

require "fix/its"

Fix :Team do
  its(:size) { MUST eq 3 }
  its(:first) { MUST eq "Ada" }
  its(:include?, "Linus") { MUST be_true }
  its(:join, ", ") { MUST eq "Ada, Grace, Linus" }

  on :last do
    its(:length) { MUST eq 5 }
  end
end

exit(Fix[:Team].test { %w[Ada Grace Linus] })

ruby team_fix.rb
team_fix.rb:4: Success: expected 3 to eq 3
team_fix.rb:5: Success: expected "Ada" to eq "Ada"
team_fix.rb:6: Success: expected true to be true
team_fix.rb:7: Success: expected "Ada, Grace, Linus" to eq "Ada, Grace, Linus"
team_fix.rb:10: Success: expected 5 to eq 5

its(:size) { MUST eq 3 } is on(:size) { it MUST eq 3 }, and the line points at the its.

• its takes the name of the method and its arguments, as on does: its(:join, ", ").
• Its block gives the requirement, a level and a matcher, and is read with the rest of the document. A block that gives anything else, or no block, raises ArgumentError when the file is loaded.
• Inside an on or a with, its sends its method to the value of that context: above, the length of the last name.
• its is a word of the language, so a let cannot take that name.

Since Ruby 3.4, a bare it in a block is its parameter: in its(:size) { MUST eq it }, it is nil. On Ruby 3.3, it is the word of Fix, which raises ArgumentError for want of a requirement. Write the value.

Use its for a method and one expectation; keep on for a context with several expectations, a with, or a further on inside it.