diff --git a/README.md b/README.md
index 3762a27..c269cfa 100644
--- a/README.md
+++ b/README.md
@@ -29,15 +29,23 @@ Or install it yourself as:
 Basic synopsis:
 
 ```ruby
-Capsicum.in_capability_mode?    # => false
-Capsicum.enter!        # => true
-Capsicum.in_capability_mode?    # => true
+require "capsicum"
 
-File.new("/dev/null")  # => Errno::ECAPMODE: Not permitted in capability mode @ rb_sysopen - /dev/null
-TCPSocket.new("0", 80) # => Errno::ECAPMODE: Not permitted in capability mode - connect(2) for "0" port 80
-`rm -rf /`             # => Errno::ECAPMODE: Not permitted in capability mode - rm
-system "rm -rf /"      # => nil
-require 'time'         # => LoadError: cannot load such file -- time
+print "In capability mode: ", Capsicum.in_capability_mode? ? "yes" : "no", "\n"
+print "Enter capability mode: ", Capsicum.enter! ? "ok" : "error", "\n"
+print "In capability mode: ", Capsicum.in_capability_mode? ? "yes" : "no", "\n"
+
+begin
+  File.new(File::NULL)
+rescue Errno::ECAPMODE => ex
+  print "Error: #{ex.message} (#{ex.class})", "\n"
+end
+
+##
+# In capability mode: no
+# Enter capability mode: ok
+# In capability mode: yes
+# Error: Not permitted in capability mode @ rb_sysopen - /dev/null (Errno::ECAPMODE)
 ```
 
 i.e. anything that involves opening a file, connecting a socket, or executing a
diff --git a/Rakefile b/Rakefile
index d949205..24c37f4 100644
--- a/Rakefile
+++ b/Rakefile
@@ -2,10 +2,7 @@ require "bundler/setup"
 require "bundler/gem_tasks"
 require "rake/testtask"
 
-Rake::TestTask.new(:test) do |t|
-  t.libs << "test"
-  t.libs << "lib"
-  t.test_files = FileList['test/**/*_test.rb']
+task :test do
+  sh "bin/test-runner"
 end
-
 task :default => :test
diff --git a/bin/test-runner b/bin/test-runner
new file mode 100755
index 0000000..feef3fe
--- /dev/null
+++ b/bin/test-runner
@@ -0,0 +1,6 @@
+#!/bin/sh
+set -e
+
+for t in test/*_test.rb; do
+    ruby -Itest "${t}"
+done
diff --git a/capsicum.gemspec b/capsicum.gemspec
index 5b70b68..0cb4be7 100644
--- a/capsicum.gemspec
+++ b/capsicum.gemspec
@@ -33,4 +33,5 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "rake", "~> 13.2"
   spec.add_development_dependency "minitest", "~> 5.0"
   spec.add_development_dependency "standard", "~> 1.38"
+  spec.add_development_dependency "test-cmd.rb", "~> 0.12"
 end
diff --git a/share/ruby-capsicum/examples/1_capability_mode_example.rb b/share/ruby-capsicum/examples/1_capability_mode_example.rb
new file mode 100644
index 0000000..b1e601b
--- /dev/null
+++ b/share/ruby-capsicum/examples/1_capability_mode_example.rb
@@ -0,0 +1,18 @@
+require "bundler/setup"
+require "capsicum"
+
+print "In capability mode: ", Capsicum.in_capability_mode? ? "yes" : "no", "\n"
+print "Enter capability mode: ", Capsicum.enter! ? "ok" : "error", "\n"
+print "In capability mode: ", Capsicum.in_capability_mode? ? "yes" : "no", "\n"
+
+begin
+  File.new(File::NULL)
+rescue Errno::ECAPMODE => ex
+  print "Error: #{ex.message} (#{ex.class})", "\n"
+end
+
+##
+# In capability mode: no
+# Enter capability mode: ok
+# In capability mode: yes
+# Error: Not permitted in capability mode @ rb_sysopen - /dev/null (Errno::ECAPMODE)
diff --git a/test/readme_test.rb b/test/readme_test.rb
new file mode 100644
index 0000000..e3a3522
--- /dev/null
+++ b/test/readme_test.rb
@@ -0,0 +1,22 @@
+require "test_helper"
+require "test-cmd"
+
+class ReadMeTest < Minitest::Test
+  def test_1_capability_mode_example
+    r = ruby(readme_example("1_capability_mode_example.rb"))
+    assert_match %r|In capability mode: no\n|, r.stdout
+    assert_match %r|Enter capability mode: ok\n|, r.stdout
+    assert_match %r|In capability mode: yes\n|, r.stdout
+    assert_match %r|Error:.+\(Errno::ECAPMODE\)\n|, r.stdout
+  end
+
+  private
+
+  def ruby(*argv)
+    cmd("ruby", *argv)
+  end
+
+  def readme_example(example_name)
+    File.join(__dir__, "..", "share", "ruby-capsicum", "examples", example_name)
+  end
+end
diff --git a/test/test_helper.rb b/test/test_helper.rb
index ea4bfc2..8684446 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -1,3 +1,4 @@
 require "bundler/setup"
+require "test-cmd"
 require "capsicum"
 require "minitest/autorun"