Current progress

koans/about_exceptions.rb

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+require File.expand_path(File.dirname(__FILE__) + '/neo')
+
+class AboutExceptions < Neo::Koan
+
+  class MySpecialError < RuntimeError
+  end
+
+  def test_exceptions_inherit_from_Exception
+    assert_equal __, MySpecialError.ancestors[1]
+    assert_equal __, MySpecialError.ancestors[2]
+    assert_equal __, MySpecialError.ancestors[3]
+    assert_equal __, MySpecialError.ancestors[4]
+  end
+
+  def test_rescue_clause
+    result = nil
+    begin
+      fail "Oops"
+    rescue StandardError => ex
+      result = :exception_handled
+    end
+
+    assert_equal __, result
+
+    assert_equal __, ex.is_a?(StandardError), "Should be a Standard Error"
+    assert_equal __, ex.is_a?(RuntimeError),  "Should be a Runtime Error"
+
+    assert RuntimeError.ancestors.include?(StandardError),
+      "RuntimeError is a subclass of StandardError"
+
+    assert_equal __, ex.message
+  end
+
+  def test_raising_a_particular_error
+    result = nil
+    begin
+      # 'raise' and 'fail' are synonyms
+      raise MySpecialError, "My Message"
+    rescue MySpecialError => ex
+      result = :exception_handled
+    end
+
+    assert_equal __, result
+    assert_equal __, ex.message
+  end
+
+  def test_ensure_clause
+    result = nil
+    begin
+      fail "Oops"
+    rescue StandardError
+      # no code here
+    ensure
+      result = :always_run
+    end
+
+    assert_equal __, result
+  end
+
+  # Sometimes, we must know about the unknown
+  def test_asserting_an_error_is_raised
+    # A do-end is a block, a topic to explore more later
+    assert_raise(___) do
+      raise MySpecialError.new("New instances can be raised directly.")
+    end
+  end
+
+end