Migrate Linter test case for valid release data

Author: stomar

test/fixtures/ok/_data/releases.yml

@@ -1,3 +0,0 @@
-- version: 2.7.0
-  date: 2018-01-01
-  post: /en/news/2018/01/01/ok/

test/test_linter_valid_release_data.rb

@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+require "helper"
+require "linter"
+
+
+describe Linter do
+
+  before do
+    chdir_tempdir
+
+    @ok = "Checking markdown files... ok\n"
+  end
+
+  after do
+    teardown_tempdir
+  end
+
+  it "checks ok valid release data with corresponding post" do
+    releases_content = <<~YAML
+      - version: 2.7.0
+        date: 2018-01-01
+        post: /en/news/2018/01/01/post/
+    YAML
+
+    post_content = <<~POST
+      ---
+      layout: news_post
+      title: "Post"
+      author: "stomar"
+      translator:
+      date: 2018-01-01 12:00:00 +0000
+      lang: en
+      ---
+
+      Content
+    POST
+
+    create_file("_data/releases.yml", releases_content)
+    create_file("en/news/_posts/2018-01-01-post.md", post_content)
+    _(linter_output).must_equal @ok
+  end
+end