data_file as an activemodel so we can have easy sweet validations

app/assets/stylesheets/custom.css.scss

@@ -117,3 +117,16 @@ input, textarea, select, .uneditable-input {
   margin-bottom: 15px;
   @include box_sizing;
 }
+
+#error_explanation {
+  color:#f00;
+  ul {
+    list-style: none;
+    margin: 0 0 18px 0;
+  }
+}
+
+.field_with_errors {
+  @extend .control-group;
+  @extend .error;
+}

app/helpers/data_files_helper.rb

@@ -1,2 +1,12 @@
 module DataFilesHelper
+  def example_input_file_link
+   'https://raw.github.com/lschallenges/data-engineering/master/example_input.tab'
+  end
+
+  def data_file_label_content_with_link
+   raw(
+    "Please upload a tab-delimited file, like " +
+      "<a href='#{example_input_file_link}'>this</a>."
+  )
+  end
 end

app/views/data_files/new.html.haml

@@ -4,11 +4,9 @@
 .row
   .span6.offset4
     = form_for(@data_file) do |f|
+      = render 'shared/error_messages', :object => f.object
       .span6
-        = f.label :data, 'Please upload a tab-delimited file'
-        %span.help-block
-          example:
-          = link_to 'here', 'https://raw.github.com/lschallenges/data-engineering/master/example_input.tab'
+        = f.label :data, data_file_label_content_with_link
         = f.file_field :data, :class => 'input-xlarge'
       .span6
         = f.submit "Upload", :class => "btn btn-large btn-primary"

app/views/shared/_error_messages.html.haml

@@ -0,0 +1,9 @@
+- if object.errors.any?
+  #error_explanation
+    .alert.alert-error
+      The form contains
+      = pluralize(object.errors.count, "error")
+      \.
+    %ul
+    - object.errors.full_messages.each do |msg|
+      %li= msg

features/file_upload.feature

@@ -8,7 +8,6 @@ Scenario: Home Page should be the file import page
   Then I should see "Import Your Data"
   Then I should see a "Upload" button
 
-@wip
 Scenario: Not uploading a file
   When I go to the file import page
     And I click "Upload"

features/step_definitions/common_steps.rb

@@ -22,7 +22,7 @@
 end
 
 Then /^I should see (\d+) validation errors?$/ do |num|
-  expected_str = "The file contains #{num} error"
+  expected_str = "The form contains #{num} error"
   expected_str += "s" if num.to_i > 1
   page.should have_content(expected_str)
 end

spec/models/data_file_spec.rb

@@ -0,0 +1,5 @@
+require 'spec_helper'
+
+describe DataFile do
+  it_should_behave_like "ActiveModel"
+end

spec/support/active_model_lint.rb

@@ -0,0 +1,19 @@
+# From https://gist.github.com/639089
+
+shared_examples_for "ActiveModel" do
+  require 'test/unit/assertions'
+  require 'active_model/lint'
+  include Test::Unit::Assertions
+  include ActiveModel::Lint::Tests
+
+  # to_s is to support ruby-1.9
+  ActiveModel::Lint::Tests.public_instance_methods.map{|m| m.to_s}.grep(/^test/).each do |m|
+    example m.gsub('_',' ') do
+      send m
+    end
+  end
+
+  def model
+    subject
+  end
+end