rna-transcription: Update tests to expect ArgumentError if invalid input is supplied

exercises/rna-transcription/.meta/generator/rna_transcription_case.rb

@@ -1,9 +1,21 @@
 require 'generator/exercise_case'
 
 class RnaTranscriptionCase < Generator::ExerciseCase
-
   def workload
+    if expects_error?
+      assert_raises(ArgumentError) { test_case }
+    else
+      assert_equal { test_case }
+    end
+  end
+
+  private
+
+  def test_case
     "assert_equal '#{expected}', Complement.of_dna('#{dna}')"
   end
 
+  def expects_error?
+    expected.is_a? Hash
+  end
 end

exercises/rna-transcription/.meta/solutions/rna_transcription.rb

@@ -1,5 +1,6 @@
 module Complement
   def self.of_dna(strand)
-    strand =~ /[^CGTA]/ ? '' : strand.tr('CGTA', 'GCAU')
+    raise ArgumentError if strand =~ /[^CGTA]/
+    strand.tr('CGTA', 'GCAU')
   end
 end

exercises/rna-transcription/rna_transcription_test.rb

@@ -30,16 +30,16 @@ def test_rna_complement
 
   def test_correctly_handles_invalid_input_rna_instead_of_dna
     skip
-    assert_equal '', Complement.of_dna('U')
+    assert_raises(ArgumentError) { Complement.of_dna('U') }
   end
 
   def test_correctly_handles_completely_invalid_dna_input
     skip
-    assert_equal '', Complement.of_dna('XXX')
+    assert_raises(ArgumentError) { Complement.of_dna('XXX') }
   end
 
   def test_correctly_handles_partially_invalid_dna_input
     skip
-    assert_equal '', Complement.of_dna('ACGTXXXCTTAA')
+    assert_raises(ArgumentError) { Complement.of_dna('ACGTXXXCTTAA') }
   end
 end