test: Work around a Ruby 3.1 bug in Range#size

(.."z").size is supposed to return nil, but in Ruby 3.1 it returns
Infinity.

Author: schwern

.rubocop.yml

@@ -35,6 +35,9 @@ RSpec/ImplicitSubject:
 RSpec/MultipleExpectations:
   Max: 5
 
+RSpec/MultipleMemoizedHelpers:
+  Max: 10
+
 # %i[foo bar baz] is more difficult to understand than [:foo, :bar, :baz]
 Style/SymbolArray:
   Enabled: false

spec/time_range_spec.rb

@@ -8,6 +8,10 @@
   end
   let(:range) { described_class.new(first, last).by(**by) }
 
+  # Range#size is supposed to always return nil when the range
+  # isn't numeric, but some versions of Ruby have a bug.
+  let(:range_size_return) { nil }
+
   shared_examples 'it is infinite' do
     describe '#count' do
       subject { range.count }
@@ -80,7 +84,7 @@
     describe '#size' do
       subject { range.size }
 
-      it { is_expected.to be_nil }
+      it { is_expected.to eq range_size_return }
     end
   end
 
@@ -182,6 +186,9 @@
 
   context 'with no begin' do
     let(:first) { nil }
+    # Ruby 3.1 has a bug where #size returns Infinity for
+    # beginless non-Numeric ranges.
+    let(:range_size_return) { (.."z").size }
 
     it_behaves_like 'a Range'
     it_behaves_like 'it has an end'