Add exercise: rna-transcription (JuliaLang#19)

* Init exercise: rna-transcription

* Add exercise: rna-transcription

* Modified formatting and error in config for rna-transcription exercise

config.json

@@ -5,6 +5,16 @@
   "active": false,
   "test_pattern": "TODO",
   "exercises": [
+    {
+      "slug": "rna-transcription",
+      "difficulty": 1,
+      "topics": [
+        "exception handling",
+        "strings",
+        "pattern matching",
+        "filtering"
+      ]
+    },
     {
       "slug": "leap",
       "difficulty": 1,

exercises/rna-transcription/example.jl

@@ -0,0 +1,10 @@
+# Given a DNA strand, its transcribed RNA strand is formed by replacing each nucleotide with its complement:
+# G -> C, C -> G, T -> A, A -> U
+function to_rna(dna::AbstractString)
+  typeof(match(r"^[GCTA]+$", dna)) == Void && error("Invalid RNA strand")
+  # Define character associations
+  a_nucleotides = Dict('G'=>'C', 'C'=>'G', 'T'=>'A', 'A'=>'U')
+  # Replace characters using dictionary
+  map((x)->a_nucleotides[x], dna)
+end
+

exercises/rna-transcription/rna-transcription.jl

@@ -0,0 +1,4 @@
+function to_rna(dna::AbstractString)
+
+end
+

exercises/rna-transcription/runtests.jl

@@ -0,0 +1,40 @@
+using Base.Test
+
+include("rna-transcription.jl")
+
+@testset "basic transformations" begin
+  @testset "rna complement of cytosine is guanine" begin
+    @test to_rna("C") == "G"
+  end
+
+  @testset "rna complement of guanine is cytosine" begin
+    @test to_rna("G") == "C"
+  end
+
+  @testset "rna complement of thymine is adenine" begin
+    @test to_rna("T") == "A"
+  end
+
+  @testset "rna complement of adenine is uracil" begin
+    @test to_rna("A") == "U"
+  end
+end
+
+@testset "rna complement" begin
+  @test to_rna("ACGTGGTCTTAA") == "UGCACCAGAAUU"
+end
+
+@testset "error handling" begin
+  @testset "dna correctly handles invalid input" begin
+    @test_throws ErrorException to_rna("U")
+  end
+
+  @testset "dna correctly handles completely invalid input" begin
+    @test_throws ErrorException to_rna("XXX")
+  end
+
+  @testset "dna correctly handles partially invalid input" begin
+    @test_throws ErrorException to_rna("ACGTXXXCTTAA")
+  end
+end
+