Add RSpec raise_error matcher spec

spec/rspec/expectations/raise_error_matcher_spec.cr

@@ -0,0 +1,94 @@
+require "../../spec_helper"
+
+# Examples taken from:
+# https://relishapp.com/rspec/rspec-expectations/v/3-8/docs/built-in-matchers/raise-error-matcher
+# and modified to fit Spectator and Crystal.
+Spectator.describe "`raise_error` matcher" do
+  context "expect any error" do
+    # This example originally calls a non-existent method.
+    # That isn't allowed in Crystal.
+    # The example has been changed to just raise a runtime error.
+    describe "dividing by zero" do
+      it "raises" do
+        expect { 42 // 0 }.to raise_error
+      end
+    end
+  end
+
+  context "expect specific error" do
+    # Again, can't even compile if a method doesn't exist.
+    # So using a different exception here.
+    describe "dividing by zero" do
+      it "raises" do
+        expect { 42 // 0 }.to raise_error(DivisionByZeroError)
+      end
+    end
+  end
+
+  # The following examples are changed slightly.
+  # `raise Type.new(message)` is the syntax in Crystal,
+  # whereas it is `raise Type, message` in Ruby.
+  # Additionally, `StandardError` doesn't exist in Crystal,
+  # so `Exception` is used instead.
+  context "match message with a string" do
+    describe "matching error message with string" do
+      it "matches the error message" do
+        expect { raise Exception.new("this message exactly") }
+          .to raise_error("this message exactly")
+      end
+    end
+  end
+
+  context "match message with a regexp" do
+    describe "matching error message with regex" do
+      it "matches the error message" do
+        expect { raise Exception.new("my message") }
+          .to raise_error(/my mess/)
+      end
+    end
+  end
+
+  context "matching message with `with_message`" do
+    describe "matching error message with regex" do
+      it "matches the error message" do
+        expect { raise Exception.new("my message") }
+          .to raise_error.with_message(/my mess/)
+      end
+    end
+  end
+
+  context "match class + message with string" do
+    describe "matching error message with string" do
+      it "matches the error message" do
+        expect { raise Exception.new("this message exactly") }
+          .to raise_error(Exception, "this message exactly")
+      end
+    end
+  end
+
+  context "match class + message with regexp" do
+    describe "matching error message with regex" do
+      it "matches the error message" do
+        expect { raise Exception.new("my message") }
+          .to raise_error(Exception, /my mess/)
+      end
+    end
+  end
+
+  # TODO: Support passing a block to `raise_error` matcher.
+  # context "set expectations on error object passed to block" do
+  #   it "raises DivisionByZeroError" do
+  #     expect { 42 // 0 }.to raise_error do |error|
+  #       expect(error).to be_a(DivisionByZeroError)
+  #     end
+  #   end
+  # end
+
+  context "expect no error at all" do
+    describe "#to_s" do
+      it "does not raise" do
+        expect { 42.to_s }.not_to raise_error
+      end
+    end
+  end
+end