WIP: tests: Add tests for issue #670.

They fail as follows:

    ZSH_PATCHLEVEL=debian/5.7.1-1
    Running test brackets
    Running test main
    # parameter-value-contains-command-position1
    1..2
    not ok 1 - [1,7] «$foobar» - expected (1 7 "assign"), observed (1 7 "unknown-token").
    ok 2 - cardinality check
    # parameter-value-contains-command-position2
    1..2
    not ok 1 - [1,2] «$y» - expected (1 2 "assign"), observed (1 2 "unknown-token").
    ok 2 - cardinality check

(The "unknown-token" was printed by the `_zsh_highlight_main_add_region_highlight`
call on line 967, after the loop.)

Before the parent commit, they behaved as follows (note the "BUG:" and
"Bail out!" on the first one — that's issue #670.2):

    ZSH_PATCHLEVEL=debian/5.7.1-1
    # parameter-value-contains-command-position1
    1..2
    ok 1 - [1,7] «$foobar» - # TODO "issue #670"
    not ok 2 - have 1 expectations and 6 region_highlight entries: «expected_region_highlight=( '1 7 assign "issue ♯670"' )» «region_highlight=( '0 7 assign' '2 7 default' '2 7 command-substitution-unquoted'
    zsh-syntax-highlighting: BUG: _zsh_highlight_highlighter_main_paint: start(2) >= end(2)
    Bail out! On './highlighters/main/test-data/parameter-value-contains-command-position2.zsh': output on stderr
    # parameter-value-contains-command-position2
    1..2
    ok 1 - [1,2] «$y» - # TODO "issue #670"
    ok 2 - cardinality check

Author: danielshahaf

highlighters/main/test-data/parameter-value-contains-command-position1.zsh

@@ -0,0 +1,38 @@
+#!/usr/bin/env zsh
+# -------------------------------------------------------------------------------------------------
+# Copyright (c) 2020 zsh-syntax-highlighting contributors
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without modification, are permitted
+# provided that the following conditions are met:
+#
+#  * Redistributions of source code must retain the above copyright notice, this list of conditions
+#    and the following disclaimer.
+#  * Redistributions in binary form must reproduce the above copyright notice, this list of
+#    conditions and the following disclaimer in the documentation and/or other materials provided
+#    with the distribution.
+#  * Neither the name of the zsh-syntax-highlighting contributors nor the names of its contributors
+#    may be used to endorse or promote products derived from this software without specific prior
+#    written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+# FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
+# IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+# -------------------------------------------------------------------------------------------------
+# -*- mode: zsh; sh-indentation: 2; indent-tabs-mode: nil; sh-basic-offset: 2; -*-
+# vim: ft=zsh sw=2 ts=2 et
+# -------------------------------------------------------------------------------------------------
+
+local foobar='x=$(ls)'
+
+BUFFER=$'$foobar'
+
+expected_region_highlight=(
+  # Used to highlight the "ba" as 'command' because the 'ls' showed through; issues #670 and #674
+  '1 7 assign' # $foobar
+)

highlighters/main/test-data/parameter-value-contains-command-position2.zsh

@@ -0,0 +1,38 @@
+#!/usr/bin/env zsh
+# -------------------------------------------------------------------------------------------------
+# Copyright (c) 2020 zsh-syntax-highlighting contributors
+# All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without modification, are permitted
+# provided that the following conditions are met:
+#
+#  * Redistributions of source code must retain the above copyright notice, this list of conditions
+#    and the following disclaimer.
+#  * Redistributions in binary form must reproduce the above copyright notice, this list of
+#    conditions and the following disclaimer in the documentation and/or other materials provided
+#    with the distribution.
+#  * Neither the name of the zsh-syntax-highlighting contributors nor the names of its contributors
+#    may be used to endorse or promote products derived from this software without specific prior
+#    written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
+# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+# FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER
+# IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+# -------------------------------------------------------------------------------------------------
+# -*- mode: zsh; sh-indentation: 2; indent-tabs-mode: nil; sh-basic-offset: 2; -*-
+# vim: ft=zsh sw=2 ts=2 et
+# -------------------------------------------------------------------------------------------------
+
+local y='x=$(ls)'
+
+BUFFER=$'$y'
+
+expected_region_highlight=(
+  # Used to trigger a "BUG" message on stderr - issues #670 and #674
+  '1 2 assign' # $y
+)