Cf. #604: Added vader test

test/vader/fold.vader

@@ -0,0 +1,33 @@
+Execute (Setup):
+  let g:vimtex_fold_enabled = 1
+
+Given tex (fold: commands):
+  \documentclass{article}
+
+  \newenvironment{ccd}{%
+    \begin{centered}\begin{tikzcd}}
+    {\end{tikzcd}\end{centered}%
+  }
+
+  \newenvironment{ccd}
+    {\begin{centered}\begin{tikzcd}}
+    {\end{tikzcd}\end{centered}}
+
+  % this should not be folded.
+  \begin{document}
+
+  \end{document}
+
+Execute (fold: verify):
+  VimtexReload
+  AssertEqual foldlevel(1),  1, 'preamble start'
+  AssertEqual foldlevel(3),  2, 'newenvironment start'
+  AssertEqual foldlevel(6),  2, 'newenvironment end pre'
+  AssertEqual foldlevel(7),  1, 'newenvironment end post'
+  AssertEqual foldlevel(8),  1, 'newenvironment - not folded'
+  AssertEqual foldlevel(12), 1, 'preamble end pre'
+  AssertEqual foldlevel(13), 0, 'preamble end post'
+
+Given:
+Execute (Cleanup):
+  unlet g:vimtex_fold_enabled