Raise better error when mjml binary is not found

lib/mjml.rb

@@ -5,6 +5,8 @@
 
 # MJML library for ruby
 module MJML
+  class BinaryNotFound < StandardError; end
+
   # Constants
   MIME_TYPE = 'text/mjml'.freeze
   EXTENSION = '.mjml'.freeze
@@ -62,6 +64,8 @@ def self.extract_executable_version
     end
 
     match.nil? ? nil : match[1]
+  rescue Errno::ENOENT => _e
+    raise BinaryNotFound, 'mjml binary not found'
   end
 
   def self.logger

spec/mjml_spec.rb

@@ -0,0 +1,20 @@
+require_relative 'spec_helper'
+require 'mjml'
+
+describe 'MJML' do
+  describe '#extract_executable_version' do
+    it 'should return the version if mjml is installed' do
+      MJML.extract_executable_version.must_be_instance_of String
+    end
+
+    it 'should return false for unknown feature' do
+      _bin_path = MJML.config.bin_path
+      MJML.config.bin_path = '/usr/bin/env mjml-not-installed'
+
+      error = -> { MJML.extract_executable_version }.must_raise MJML::BinaryNotFound
+      error.message.must_equal 'mjml binary not found'
+
+      MJML.config.bin_path = _bin_path
+    end
+  end
+end