I broke up with neovim....vim is my best friend now

dot_vim/plugged/vimtex/test/test-subfiles/Makefile

@@ -0,0 +1,14 @@
+MYVIM ?= nvim --clean --headless
+
+INMAKE := 1
+export INMAKE
+
+TESTS := $(wildcard test*.vim)
+TESTS := $(TESTS:.vim=)
+
+.PHONY: default $(TESTS)
+
+default: $(TESTS)
+
+$(TESTS):
+	@$(MYVIM) -u $@.vim

dot_vim/plugged/vimtex/test/test-subfiles/test_nested.vim

@@ -0,0 +1,19 @@
+set nocompatible
+let &rtp = '../..,' . &rtp
+filetype plugin on
+
+call vimtex#log#set_silent()
+
+nnoremap q :qall!<cr>
+
+silent edit test_nested/parts/chapter.tex
+call assert_equal(expand('%:p:h:h'), b:vimtex.root)
+silent VimtexToggleMain
+call assert_equal(expand('%:p:h'), b:vimtex.root)
+
+silent edit test_nested/parts/sections/first.tex
+call assert_equal(expand('%:p:h:h:h'), b:vimtex.root)
+silent VimtexToggleMain
+call assert_equal(expand('%:p:h'), b:vimtex.root)
+
+call vimtex#test#finished()

dot_vim/plugged/vimtex/test/test-subfiles/test_nested/main.tex

@@ -0,0 +1,9 @@
+\documentclass[a4paper]{report}
+\usepackage{subfiles}
+
+\begin{document}
+\tableofcontents
+
+\subfile{parts/chapter.tex}
+
+\end{document}

dot_vim/plugged/vimtex/test/test-subfiles/test_nested/parts/chapter.tex

@@ -0,0 +1,7 @@
+\documentclass[../main.tex]{subfiles}
+\begin{document}
+\chapter{Chapter with subsections}
+Here we introduce the bug as it currently is experienced by a user.
+\subfile{sections/first.tex}
+\subfile{sections/second.tex}
+\end{document}

dot_vim/plugged/vimtex/test/test-subfiles/test_nested/parts/sections/first.tex

@@ -0,0 +1,10 @@
+\documentclass[../../main.tex]{subfiles}
+\begin{document}
+
+\section{The first section}
+Titling notwithstanding, could this issue be a case of PEBCAC?
+
+\subsection{A subsection}
+Hello world.
+
+\end{document}

dot_vim/plugged/vimtex/test/test-subfiles/test_nested/parts/sections/second.tex

@@ -0,0 +1,5 @@
+\documentclass[../../main.tex]{subfiles}
+\begin{document}
+\section{The second section}
+You don't always think it be like this, but it do.
+\end{document}