add spec for filters class

lib/jekyll-seo-tag/drop.rb

@@ -2,6 +2,9 @@ module Jekyll
   class SeoTag
     class Drop < Jekyll::Drops::Drop
       TITLE_SEPARATOR = " | ".freeze
+      FORMAT_STRING_METHODS = %i[
+        markdownify strip_html normalize_whitespace escape_once
+      ].freeze
 
       def initialize(text, context)
         @obj = {}
@@ -190,8 +193,7 @@ module Jekyll
       end
 
       def format_string(string)
-        methods = %i[markdownify strip_html normalize_whitespace escape_once]
-        methods.each do |method|
+        FORMAT_STRING_METHODS.each do |method|
           string = filters.public_send(method, string)
         end
 

spec/jekyll_seo_tag/filters_spec.rb

@@ -0,0 +1,18 @@
+RSpec.describe Jekyll::SeoTag::Filters do
+  let(:page)      { make_page }
+  let(:site)      { make_site }
+  let(:context)   { make_context(:page => page, :site => site) }
+  subject { described_class.new(context) }
+
+  it "stores the context" do
+    expect(subject.instance_variable_get("@context")).to be_a(Liquid::Context)
+  end
+
+  it "exposes jekyll filters" do
+    expect(subject).to respond_to(:markdownify)
+  end
+
+  it "exposes liquid standard filters" do
+    expect(subject).to respond_to(:normalize_whitespace)
+  end
+end