Add tests for assets directory support.

test/fixtures/test-theme/assets/img/another-logo.png

@@ -0,0 +1 @@
+logo.png

test/fixtures/test-theme/assets/style.scss

@@ -0,0 +1,3 @@
+---
+---
+@import "test-theme-{{ site.theme-color }}";

test/test_theme.rb

@@ -34,9 +34,9 @@ class TestTheme < JekyllUnitTest
   end
 
   context "path generation" do
-    [:layouts, :includes, :sass].each do |folder|
+    [:assets, :_layouts, :_includes, :_sass].each do |folder|
       should "know the #{folder} path" do
-        expected = File.expand_path("_#{folder}", @expected_root)
+        expected = File.expand_path(folder.to_s, @expected_root)
         assert_equal expected, @theme.public_send("#{folder}_path")
       end
     end

test/test_theme_assets_reader.rb

@@ -0,0 +1,61 @@
+require "helper"
+
+class TestThemeAssetsReader < JekyllUnitTest
+  def setup
+    @site = fixture_site(
+      "theme" => "test-theme",
+      "theme-color" => "black"
+    )
+    assert @site.theme
+  end
+
+  def assert_file_with_relative_path(haystack, relative_path)
+      assert haystack.any? { |f|
+        f.relative_path == relative_path
+      }, "Site should read in the #{relative_path} file, but it was not found in #{haystack.inspect}"
+  end
+
+  def refute_file_with_relative_path(haystack, relative_path)
+      refute haystack.any? { |f|
+        f.relative_path == relative_path
+      }, "Site should not have read in the #{relative_path} file, but it was found in #{haystack.inspect}"
+  end
+
+  context "with a valid theme" do
+    should "read all assets" do
+      ThemeAssetsReader.new(@site).read
+      assert_file_with_relative_path @site.static_files, "assets/img/logo.png"
+      assert_file_with_relative_path @site.pages, "assets/style.scss"
+    end
+
+    should "convert pages" do
+      @site.process
+
+      file = @site.pages.find { |f| f.relative_path == "assets/style.scss" }
+      refute_nil file
+      assert_equal @site.in_dest_dir("assets/style.css"), file.destination(@site.dest)
+      assert_includes file.output, ".sample {\n  color: black; }"
+    end
+  end
+
+  context "with a valid theme without an assets dir" do
+    should "not read any assets" do
+      allow(Theme).to receive(:realpath_for).with(:sass).and_return(nil)
+      site = fixture_site("theme" => "test-theme")
+      ThemeAssetsReader.new(site).read
+      refute_file_with_relative_path @site.static_files, "assets/img/logo.png"
+      refute_file_with_relative_path @site.pages, "assets/style.scss"
+    end
+  end
+
+  context "with no theme" do
+    should "not read any assets" do
+      site = fixture_site("theme" => nil)
+      ThemeAssetsReader.new(site).read
+      refute_file_with_relative_path @site.static_files, "assets/img/logo.png"
+      refute_file_with_relative_path @site.pages, "assets/style.scss"
+    end
+
+  end
+
+end