Add comparison tests from RSpec docs

spec/rspec/expectations/comparison_matchers_spec.cr

@@ -0,0 +1,47 @@
+require "../../spec_helper"
+
+# Examples taken from:
+# https://relishapp.com/rspec/rspec-expectations/v/3-8/docs/built-in-matchers/comparison-matchers
+# and modified to fit Spectator and Crystal.
+Spectator.describe "Comparison matchers" do
+  context "numeric operator matchers" do
+    describe 18 do
+      it { is_expected.to be < 20 }
+      it { is_expected.to be > 15 }
+      it { is_expected.to be <= 19 }
+      it { is_expected.to be >= 17 }
+
+      # deliberate failures
+      # TODO: Add support for expected failures.
+      xit { is_expected.to be < 15 }
+      xit { is_expected.to be > 20 }
+      xit { is_expected.to be <= 17 }
+      xit { is_expected.to be >= 19 }
+      # it { is_expected.to be < 'a' } # Removed because Crystal doesn't support Int32#<(Char)
+    end
+
+    describe 'a' do
+      it { is_expected.to be < 'b' }
+
+      # deliberate failures
+      # TODO: Add support for expected failures.
+      # it { is_expected.to be < 18 } # Removed because Crystal doesn't support Char#<(Int32)
+    end
+  end
+
+  context "string operator matchers" do
+    describe "Strawberry" do
+      it { is_expected.to be < "Tomato" }
+      it { is_expected.to be > "Apple" }
+      it { is_expected.to be <= "Turnip" }
+      it { is_expected.to be >= "Banana" }
+
+      # deliberate failures
+      # TODO: Add support for expected failures.
+      xit { is_expected.to be < "Cranberry" }
+      xit { is_expected.to be > "Zuchini" }
+      xit { is_expected.to be <= "Potato" }
+      xit { is_expected.to be >= "Tomato" }
+    end
+  end
+end