#3633 - Move linter tests into test/linter

test/linter/test_markdown_markdownlint.vader

@@ -0,0 +1,13 @@
+Before:
+  call ale#assert#SetUpLinterTest('markdown', 'markdownlint')
+
+After:
+  call ale#assert#TearDownLinterTest()
+
+Execute(The default command should be correct):
+  AssertLinter 'markdownlint', ale#Escape('markdownlint') . ' %s'
+
+Execute(The options should be configurable):
+  let g:ale_markdown_markdownlint_options = '--config ~/custom/.markdownlintrc'
+
+  AssertLinter 'markdownlint', ale#Escape('markdownlint') . ' --config ~/custom/.markdownlintrc %s'