Add failing tests for SetexToAtx

Author: lggruspe

test/header-decrease.vader

@@ -89,3 +89,28 @@ Expect (no changes):
   ##### e
 
   ###### f
+
+Given markdown;
+a
+=
+
+b
+-
+
+Execute (HeaderIncrease with setext headers):
+  :HeaderIncrease
+
+Expect (convert to atx headers):
+  ## a
+
+  ### b
+
+Given markdown;
+a
+-
+
+Execute (HeaderDecrease with setext headers):
+  :HeaderDecrease
+
+Expect (convert to atx headers):
+  # a

test/setextoatx.vader

@@ -0,0 +1,22 @@
+Given markdown;
+# a
+
+a
+=
+
+## b
+
+b
+-
+
+Execute (SetexToAtx):
+  :SetexToAtx
+
+Expect (convert setex-style headings to atx):
+  # a
+
+  # a
+
+  ## b
+
+  ## b