diff --git a/spec/std/spec/expectations_spec.cr b/spec/std/spec/expectations_spec.cr
index 0831bca226ca..2e7e9d8df57f 100644
--- a/spec/std/spec/expectations_spec.cr
+++ b/spec/std/spec/expectations_spec.cr
@@ -12,6 +12,16 @@ private record NoObjectId, to_unsafe : Int32 do
   end
 end
 
+private class ExceptionWithOverriddenToS < Exception
+  def initialize(message : String, @to_s : String)
+    super(message)
+  end
+
+  def to_s
+    @to_s
+  end
+end
+
 describe "expectations" do
   describe "accept a custom failure message" do
     it { 1.should be < 3, "custom message!" }
@@ -169,8 +179,212 @@ describe "expectations" do
   end
 
   describe "expect_raises" do
-    it "pass if raises MyError" do
+    it "passes if expected message equals actual message and expected class equals actual class" do
       expect_raises(Exception, "Ops") { raise Exception.new("Ops") }
     end
+
+    it "passes if expected message equals actual message and expected class is an ancestor of actual class" do
+      expect_raises(Exception, "Ops") { raise ArgumentError.new("Ops") }
+    end
+
+    it "passes if expected message is a substring of actual message and expected class equals actual class" do
+      expect_raises(Exception, "Ops") { raise Exception.new("Black Ops") }
+    end
+
+    it "passes if expected message is a substring of actual message and expected class is an ancestor of actual class" do
+      expect_raises(Exception, "Ops") { raise ArgumentError.new("Black Ops") }
+    end
+
+    it "passes if expected regex matches actual message and expected class equals actual class" do
+      expect_raises(Exception, /Ops/) { raise Exception.new("Black Ops") }
+    end
+
+    it "passes if expected regex matches actual message and expected class is an ancestor of actual class" do
+      expect_raises(Exception, /Ops/) { raise ArgumentError.new("Black Ops") }
+    end
+
+    it "passes if given no message expectation and expected class equals actual class" do
+      expect_raises(Exception) { raise Exception.new("Ops") }
+    end
+
+    it "passes if given no message expectation and expected class is an ancestor of actual class" do
+      expect_raises(Exception) { raise ArgumentError.new("Ops") }
+    end
+
+    it "passes if given no message expectation, actual message is nil and expected class equals actual class" do
+      expect_raises(Exception) { raise Exception.new(nil) }
+    end
+
+    it "passes if given no message expectation, actual message is nil and expected class is an ancestor of actual class" do
+      expect_raises(Exception) { raise ArgumentError.new(nil) }
+    end
+
+    it "fails if expected message does not equal actual message and expected class equals actual class" do
+      expect_raises(Exception, "Ops") { raise Exception.new("Hm") }
+    rescue Spec::AssertionFailed
+      # success
+    else
+      fail "expected Spec::AssertionFailed but nothing was raised"
+    end
+
+    it "fails if given expected message, actual message is nil and expected class equals actual class" do
+      expect_raises(Exception, "Ops") { raise Exception.new(nil) }
+    rescue Spec::AssertionFailed
+      # success
+    else
+      fail "expected Spec::AssertionFailed but nothing was raised"
+    end
+
+    it "fails if expected regex does not match actual message and expected class equals actual class" do
+      expect_raises(Exception, /Ops/) { raise Exception.new("Hm") }
+    rescue Spec::AssertionFailed
+      # success
+    else
+      fail "expected Spec::AssertionFailed but nothing was raised"
+    end
+
+    it "fails if given expected regex, actual message is nil and expected class equals actual class" do
+      expect_raises(Exception, /Ops/) { raise Exception.new(nil) }
+    rescue Spec::AssertionFailed
+      # success
+    else
+      fail "expected Spec::AssertionFailed but nothing was raised"
+    end
+
+    it "fails if given no message expectation and expected class does not equal and is not an ancestor of actual class" do
+      expect_raises(IndexError) { raise ArgumentError.new("Ops") }
+    rescue Spec::AssertionFailed
+      # success
+    else
+      fail "expected Spec::AssertionFailed but nothing was raised"
+    end
+
+    it "fails if given no message expectation, actual message is nil and expected class does not equal and is not an ancestor of actual class" do
+      expect_raises(IndexError) { raise ArgumentError.new(nil) }
+    rescue Spec::AssertionFailed
+      # success
+    else
+      fail "expected Spec::AssertionFailed but nothing was raised"
+    end
+
+    it "fails if nothing was raised" do
+      expect_raises(IndexError) { raise ArgumentError.new("Ops") }
+    rescue Spec::AssertionFailed
+      # success
+    else
+      fail "expected Spec::AssertionFailed but nothing was raised"
+    end
+
+    it "uses the exception's #to_s output to match a given String" do
+      expect_raises(Exception, "Hm") { raise ExceptionWithOverriddenToS.new("Ops", to_s: "Hm") }
+    end
+
+    it "uses the exception's #to_s output to match a given Regex" do
+      expect_raises(Exception, /Hm/) { raise ExceptionWithOverriddenToS.new("Ops", to_s: "Hm") }
+    end
+
+    describe "failure message format" do
+      context "given string to compare with message" do
+        it "contains expected exception, actual exception and backtrace" do
+          expect_raises(Exception, "digits should be non-negative") do
+            raise IndexError.new("Index out of bounds")
+          end
+        rescue e : Spec::AssertionFailed
+          # don't check backtrace items because they are platform specific
+          e.message.as(String).should contain(<<-MESSAGE)
+            Expected Exception with message containing: "digits should be non-negative"
+                 got IndexError with message: "Index out of bounds"
+            Backtrace:
+            MESSAGE
+        else
+          fail "expected Spec::AssertionFailed but nothing is raised"
+        end
+
+        it "contains expected class, actual exception and backtrace when expected class does not match actual class" do
+          expect_raises(ArgumentError, "digits should be non-negative") do
+            raise IndexError.new("Index out of bounds")
+          end
+        rescue e : Spec::AssertionFailed
+          # don't check backtrace items because they are platform specific
+          e.message.as(String).should contain(<<-MESSAGE)
+            Expected ArgumentError
+                 got IndexError with message: "Index out of bounds"
+            Backtrace:
+            MESSAGE
+        else
+          fail "expected Spec::AssertionFailed but nothing is raised"
+        end
+
+        it "escapes expected and actual messages in the same way" do
+          expect_raises(Exception, %q(a\tb\nc)) do
+            raise %q(a\tb\nc).inspect
+          end
+        rescue e : Spec::AssertionFailed
+          e.message.as(String).should contain("Expected Exception with message containing: #{%q(a\tb\nc).inspect}")
+          e.message.as(String).should contain("got Exception with message: #{%q(a\tb\nc).inspect.inspect}")
+        else
+          fail "expected Spec::AssertionFailed but nothing is raised"
+        end
+      end
+
+      context "given regex to match a message" do
+        it "contains expected exception, actual exception and backtrace" do
+          expect_raises(Exception, /digits should be non-negative/) do
+            raise IndexError.new("Index out of bounds")
+          end
+        rescue e : Spec::AssertionFailed
+          # don't check backtrace items because they are platform specific
+          e.message.as(String).should contain(<<-MESSAGE)
+            Expected Exception with message matching: /digits should be non-negative/
+                 got IndexError with message: "Index out of bounds"
+            Backtrace:
+            MESSAGE
+        else
+          fail "expected Spec::AssertionFailed but nothing is raised"
+        end
+
+        it "contains expected class, actual exception and backtrace when expected class does not match actual class" do
+          expect_raises(ArgumentError, /digits should be non-negative/) do
+            raise IndexError.new("Index out of bounds")
+          end
+        rescue e : Spec::AssertionFailed
+          # don't check backtrace items because they are platform specific
+          e.message.as(String).should contain(<<-MESSAGE)
+            Expected ArgumentError
+                 got IndexError with message: "Index out of bounds"
+            Backtrace:
+            MESSAGE
+        else
+          fail "expected Spec::AssertionFailed but nothing is raised"
+        end
+      end
+
+      context "given nil to allow any message" do
+        it "contains expected class, actual exception and backtrace when expected class does not match actual class" do
+          expect_raises(ArgumentError, nil) do
+            raise IndexError.new("Index out of bounds")
+          end
+        rescue e : Spec::AssertionFailed
+          # don't check backtrace items because they are platform specific
+          e.message.as(String).should contain(<<-MESSAGE)
+            Expected ArgumentError
+                 got IndexError with message: "Index out of bounds"
+            Backtrace:
+            MESSAGE
+        else
+          fail "expected Spec::AssertionFailed but nothing is raised"
+        end
+      end
+
+      context "nothing was raises" do
+        it "contains expected class" do
+          expect_raises(IndexError) { }
+        rescue e : Spec::AssertionFailed
+          e.message.as(String).should contain("Expected IndexError but nothing was raised")
+        else
+          fail "expected Spec::AssertionFailed but nothing was raised"
+        end
+      end
+    end
   end
 end
diff --git a/src/spec/expectations.cr b/src/spec/expectations.cr
index 158c82413fc5..79cad0680417 100644
--- a/src/spec/expectations.cr
+++ b/src/spec/expectations.cr
@@ -410,19 +410,17 @@ module Spec
           raise ex
         end
 
-        ex_to_s = ex.to_s
+        exception_as_string = ex.to_s
         case message
         when Regex
-          unless (ex_to_s =~ message)
-            backtrace = ex.backtrace.join('\n') { |f| "  # #{f}" }
-            fail "Expected #{klass} with message matching #{message.pretty_inspect}, " \
-                 "got #<#{ex.class}: #{ex_to_s}> with backtrace:\n#{backtrace}", file, line
+          unless exception_as_string =~ message
+            expectation_failed_message = build_expectation_failed_message(klass, message, ex, exception_as_string)
+            fail expectation_failed_message, file, line
           end
         when String
-          unless ex_to_s.includes?(message)
-            backtrace = ex.backtrace.join('\n') { |f| "  # #{f}" }
-            fail "Expected #{klass} with #{message.pretty_inspect}, got #<#{ex.class}: " \
-                 "#{ex_to_s}> with backtrace:\n#{backtrace}", file, line
+          unless exception_as_string.includes?(message)
+            expectation_failed_message = build_expectation_failed_message(klass, message, ex, exception_as_string)
+            fail expectation_failed_message, file, line
           end
         when Nil
           # No need to check the message
@@ -430,12 +428,45 @@ module Spec
 
         ex
       rescue ex
-        backtrace = ex.backtrace.join('\n') { |f| "  # #{f}" }
-        fail "Expected #{klass}, got #<#{ex.class}: #{ex}> with backtrace:\n" \
-             "#{backtrace}", file, line
+        expectation_failed_message = build_expectation_failed_message(klass, ex)
+        fail expectation_failed_message, file, line
       else
         fail "Expected #{klass} but nothing was raised", file, line
       end
+
+      private def build_expectation_failed_message(klass : Class, message : String, exception : Exception, exception_as_string : String)
+        backtrace = "  # #{exception.backtrace.join("\n  # ")}"
+
+        <<-MESSAGE
+        Expected #{klass} with message containing: #{message.inspect}
+             got #{exception.class} with message: #{exception_as_string.inspect}
+        Backtrace:
+        #{backtrace}
+        MESSAGE
+      end
+
+      private def build_expectation_failed_message(klass : Class, message : Regex, exception : Exception, exception_as_string : String)
+        backtrace = "  # #{exception.backtrace.join("\n  # ")}"
+
+        <<-MESSAGE
+        Expected #{klass} with message matching: #{message.inspect}
+             got #{exception.class} with message: #{exception_as_string.inspect}
+        Backtrace:
+        #{backtrace}
+        MESSAGE
+      end
+
+      private def build_expectation_failed_message(klass : Class, exception : Exception)
+        exception_as_string = exception.to_s
+        backtrace = "  # #{exception.backtrace.join("\n  # ")}"
+
+        <<-MESSAGE
+        Expected #{klass}
+             got #{exception.class} with message: #{exception_as_string.inspect}
+        Backtrace:
+        #{backtrace}
+        MESSAGE
+      end
     {% end %}
   end