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angelikatyborska's solution

to Resistor Color in the Elixir Track

Published at Jan 12 2020 · 0 comments
Test suite

Resistors have color coded bands, where each color maps to a number. The first 2 bands of a resistor have a simple encoding scheme: each color maps to a single number.

These colors are encoded as follows:

  • Black: 0
  • Brown: 1
  • Red: 2
  • Orange: 3
  • Yellow: 4
  • Green: 5
  • Blue: 6
  • Violet: 7
  • Grey: 8
  • White: 9

Mnemonics map the colors to the numbers, that, when stored as an array, happen to map to their index in the array: Better Be Right Or Your Great Big Values Go Wrong.

Running tests

Execute the tests with:

$ mix test

Pending tests

In the test suites, all but the first test have been skipped.

Once you get a test passing, you can unskip the next one by commenting out the relevant @tag :pending with a # symbol.

For example:

# @tag :pending
test "shouting" do
  assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"

Or, you can enable all the tests by commenting out the ExUnit.configure line in the test suite.

# ExUnit.configure exclude: :pending, trace: true

If you're stuck on something, it may help to look at some of the available resources out there where answers might be found.


This is an exercise to introduce users to basic programming constructs, just after Hello World. Electronic color code Wikipedia article

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.


defmodule ResistorColorTest do
  use ExUnit.Case

  # @tag :pending
  test "returns black color code" do
    assert ResistorColor.code("black") == 0

  @tag :pending
  test "returns brown color code" do
    assert ResistorColor.code("brown") == 1

  @tag :pending
  test "returns red color code" do
    assert ResistorColor.code("red") == 2

  @tag :pending
  test "returns orange color code" do
    assert ResistorColor.code("orange") == 3

  @tag :pending
  test "returns yellow color code" do
    assert ResistorColor.code("yellow") == 4

  @tag :pending
  test "returns green color code" do
    assert ResistorColor.code("green") == 5

  @tag :pending
  test "returns blue color code" do
    assert ResistorColor.code("blue") == 6

  @tag :pending
  test "returns violet color code" do
    assert ResistorColor.code("violet") == 7

  @tag :pending
  test "returns grey color code" do
    assert ResistorColor.code("grey") == 8

  @tag :pending
  test "returns white color code" do
    assert ResistorColor.code("white") == 9

  @tag :pending
  test "returns all colors" do
    colors = [

    assert ResistorColor.colors() == colors


ExUnit.configure(exclude: :pending, trace: true)
defmodule ResistorColor do
  @moduledoc false

  @colors_to_values %{
    "black" => 0,
    "brown" => 1,
    "red" => 2,
    "orange" => 3,
    "yellow" => 4,
    "green" => 5,
    "blue" => 6,
    "violet" => 7,
    "grey" => 8,
    "white" => 9

  @spec colors() :: list(String.t())
  def colors do
    |> Map.to_list()
    |> Enum.sort_by(&elem(&1, 1))
    |> Enum.map(fn {color, _value} -> color end)

  @spec code(String.t()) :: integer()
  def code(color) do

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