Add RSpec start_with and end_with matchers specs

spec/rspec/expectations/end_with_matcher_spec.cr

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+require "../../spec_helper"
+
+# Examples taken from:
+# https://relishapp.com/rspec/rspec-expectations/v/3-8/docs/built-in-matchers/end-with-matcher
+# and modified to fit Spectator and Crystal.
+Spectator.describe "`end_with` matcher" do
+  context "string usage" do
+    describe "this string" do
+      it { is_expected.to end_with "string" }
+      it { is_expected.not_to end_with "stringy" }
+
+      # deliberate failures
+      # TODO: Add support for expected failures.
+      xit { is_expected.not_to end_with "string" }
+      xit { is_expected.to end_with "stringy" }
+    end
+  end
+
+  context "array usage" do
+    describe [0, 1, 2, 3, 4] do
+      it { is_expected.to end_with 4 }
+      # TODO: Add support for multiple items at the end of an array.
+      # it { is_expected.to end_with 3, 4 }
+      it { is_expected.not_to end_with 3 }
+      # it { is_expected.not_to end_with 0, 1, 2, 3, 4, 5 }
+
+      # deliberate failures
+      # TODO: Add support for expected failures.
+      xit { is_expected.not_to end_with 4 }
+      xit { is_expected.to end_with 3 }
+    end
+  end
+end

spec/rspec/expectations/start_with_matcher_spec.cr

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+require "../../spec_helper"
+
+# Examples taken from:
+# https://relishapp.com/rspec/rspec-expectations/v/3-8/docs/built-in-matchers/start-with-matcher
+# and modified to fit Spectator and Crystal.
+Spectator.describe "`start_with` matcher" do
+  context "with a string" do
+    describe "this string" do
+      it { is_expected.to start_with "this" }
+      it { is_expected.not_to start_with "that" }
+
+      # deliberate failures
+      # TODO: Add support for expected failures.
+      xit { is_expected.not_to start_with "this" }
+      xit { is_expected.to start_with "that" }
+    end
+  end
+
+  context "with an array" do
+    describe [0, 1, 2, 3, 4] do
+      it { is_expected.to start_with 0 }
+      # TODO: Add support for multiple items at the beginning of an array.
+      # it { is_expected.to start_with(0, 1) }
+      it { is_expected.not_to start_with(2) }
+      # it { is_expected.not_to start_with(0, 1, 2, 3, 4, 5) }
+
+      # deliberate failures
+      # TODO: Add support for expected failures.
+      xit { is_expected.not_to start_with 0 }
+      xit { is_expected.to start_with 3 }
+    end
+  end
+end