Add tests for HeaderDecrease and HeaderIncrease

Author: lggruspe

test/header-decrease.vader

@@ -0,0 +1,91 @@
+Given markdown;
+# a
+
+## b
+
+### c
+
+#### d
+
+##### e
+
+Execute (HeaderIncrease without forbidden level):
+  :HeaderIncrease
+
+Expect (increase level of all headers):
+  ## a
+
+  ### b
+
+  #### c
+
+  ##### d
+
+  ###### e
+
+Given markdown;
+# a
+
+###### b
+
+Execute (HeaderIncrease with forbidden level):
+  :HeaderIncrease
+
+Expect (no changes):
+  # a
+
+  ###### b
+
+Given markdown;
+## a
+
+### b
+
+#### c
+
+##### d
+
+###### e
+
+Execute (HeaderDecrease without forbidden level):
+  :HeaderDecrease
+
+Expect (decrease level of all headers):
+  # a
+
+  ## b
+
+  ### c
+
+  #### d
+
+  ##### e
+
+Given markdown;
+# a
+
+## b
+
+### c
+
+#### d
+
+##### e
+
+###### f
+
+Execute (HeaderDecrease with forbidden level):
+  :HeaderDecrease
+
+Expect (no changes):
+  # a
+
+  ## b
+
+  ### c
+
+  #### d
+
+  ##### e
+
+  ###### f