add spec for Range#=== to behave like Range#cover? in Ruby 2.7

[lxxxvi]

Hello again 👋

From #745 :

•  Range#=== now uses Range#cover? for String arguments, too (in Ruby 2.6, it was
  changed from Range#include? for all types except strings). Bug #15449

To cover that (pun intended), I basically just added this to Range#=== specs

it_behaves_like :range_cover_and_include, :cover?
it_behaves_like :range_cover, :cover?

Do you think this is sufficient? 🙈

[eregon]

Sounds good, sorry for the late review.

[lxxxvi]

@eregon Thanks for your review!

Interestingly some tests started to fail now (see bottom). Apparently :=== doesn't work the same as cover? when comparing with number ranges. Example

# Ruby v2.7.2

(2..5).cover?((3..4)) # => true
(2..5) === (3..4)     # => false

I am not sure if this is expected, hence if I understand the Bug #15449 description correctly.

Should :=== work exactly like .cover? or just particularly for strings?

What do you think?

Failing tests

Range#=== range argument accepts range argument FAILED
Expected false to be true
/.../core/range/shared/cover.rb:97:in `block (4 levels) in <top (required)>'
/.../core/range/case_compare_spec.rb:5:in `<top (required)>'

(0..10).send(@method, (3..7)).should be_true

---

Range#=== range argument supports boundaries of different comparable types FAILED
Expected false to be true
/.../core/range/shared/cover.rb:120:in `block (4 levels) in <top (required)>'
/.../core/range/case_compare_spec.rb:5:in `<top (required)>'

(0..10).send(@method, (3.1..7.9)).should be_true

---

Range#=== range argument honors exclusion of right boundary (:exclude_end option) FAILED
Expected false to be true
/.../core/range/shared/cover.rb:132:in `block (4 levels) in <top (required)>'
/.../core/range/case_compare_spec.rb:5:in `<top (required)>'

(0..10).send(@method, (0..10)).should be_true

[eregon]

It's expected (0..10).send(@method, (3..7)) is only true for cover? itself.
=== only has the "does the Range include that element?", not the "is this Range a superset of that Range?" semantics.

So let's move

spec/core/range/shared/cover.rb

Lines 94 to 152 in c8bc53a

	ruby_version_is "2.6" do
	context "range argument" do
	it "accepts range argument" do
	(0..10).send(@method, (3..7)).should be_true
	(0..10).send(@method, (3..15)).should be_false
	(0..10).send(@method, (-2..7)).should be_false
	(1.1..7.9).send(@method, (2.5..6.5)).should be_true
	(1.1..7.9).send(@method, (2.5..8.5)).should be_false
	(1.1..7.9).send(@method, (0.5..6.5)).should be_false
	('c'..'i').send(@method, ('d'..'f')).should be_true
	('c'..'i').send(@method, ('d'..'z')).should be_false
	('c'..'i').send(@method, ('a'..'f')).should be_false
	range_10_100 = RangeSpecs::TenfoldSucc.new(10)..RangeSpecs::TenfoldSucc.new(100)
	range_20_90 = RangeSpecs::TenfoldSucc.new(20)..RangeSpecs::TenfoldSucc.new(90)
	range_20_110 = RangeSpecs::TenfoldSucc.new(20)..RangeSpecs::TenfoldSucc.new(110)
	range_0_90 = RangeSpecs::TenfoldSucc.new(0)..RangeSpecs::TenfoldSucc.new(90)
	range_10_100.send(@method, range_20_90).should be_true
	range_10_100.send(@method, range_20_110).should be_false
	range_10_100.send(@method, range_0_90).should be_false
	end
	it "supports boundaries of different comparable types" do
	(0..10).send(@method, (3.1..7.9)).should be_true
	(0..10).send(@method, (3.1..15.9)).should be_false
	(0..10).send(@method, (-2.1..7.9)).should be_false
	end
	it "returns false if types are not comparable" do
	(0..10).send(@method, ('a'..'z')).should be_false
	(0..10).send(@method, (RangeSpecs::TenfoldSucc.new(0)..RangeSpecs::TenfoldSucc.new(100))).should be_false
	end
	it "honors exclusion of right boundary (:exclude_end option)" do
	# Integer
	(0..10).send(@method, (0..10)).should be_true
	(0...10).send(@method, (0...10)).should be_true
	(0..10).send(@method, (0...10)).should be_true
	(0...10).send(@method, (0..10)).should be_false
	(0...11).send(@method, (0..10)).should be_true
	(0..10).send(@method, (0...11)).should be_true
	# Float
	(0..10.1).send(@method, (0..10.1)).should be_true
	(0...10.1).send(@method, (0...10.1)).should be_true
	(0..10.1).send(@method, (0...10.1)).should be_true
	(0...10.1).send(@method, (0..10.1)).should be_false
	(0...11.1).send(@method, (0..10.1)).should be_true
	(0..10.1).send(@method, (0...11.1)).should be_false
	end
	end
	end

into its own describe :range_cover_subrange, shared: true do, that way we only test that for Range#cover? itself.

[lxxxvi]

@eregon Thank you for your explanation. I added a new commit according your suggestion.

[eregon]

Thank you, looks good!