tests: Set ZSH explicitly and avoid 'env'

'env -i' clears the complete environment, including PATH. In that
case, on most platforms, when excuting commands without PATH being
set, /usr/bin and /bin are searched, e.g. on Linux:

  $ strace env -i asdf |&  grep asdf
  execve("/usr/bin/env", ["env", "-i", "asdf"], 0x7ffc3e3c0890 /* 27 vars */) = 0
  execve("/bin/asdf", ["asdf"], 0x55be2da090d0 /* 0 vars */) = -1 ENOENT (No such file or directory)
  execve("/usr/bin/asdf", ["asdf"], 0x55be2da090d0 /* 0 vars */) = -1 ENOENT (No such file or directory)
  write(2, "\342\200\230asdf\342\200\231", 10‘asdf’) = 10

Howver, this does not hold on every platform. E.g. on Cygwin, so
such fallback paths are searched:

  $ strace env -i asdf |&  grep asdf
     37   25736 [main] env 3516 build_argv: argv[2] = 'asdf'
    643   30373 [main] env 3516 find_exec: find_exec (asdf)
     35   30408 [main] env 3516 find_exec: (null) = find_exec (asdf)
     36   30444 [main] env 3516 spawnve: spawnve (, asdf, 0x10040B000)
  ‘asdf’  199   53601 [main] env 3516 write: 10 = write(2, 0x10040B040, 10)

  $ env -i zsh
  env: ‘zsh’: No such file or directory

Therefore, avoid the need for 'env' to do the searching and invoke
the proper zsh binary explicitly.

Makefile

@@ -4,7 +4,7 @@ INSTALL?=install -c
 PREFIX?=/usr/local
 SHARE_DIR?=$(DESTDIR)$(PREFIX)/share/$(NAME)
 DOC_DIR?=$(DESTDIR)$(PREFIX)/share/doc/$(NAME)
-ZSH?=zsh # zsh binary to run tests with
+ZSH?="`which zsh`" # zsh binary to run tests with
 
 all:
 	cd docs && \
@@ -41,7 +41,7 @@ test:
 	for test in highlighters/*; do \
 		if [ -d $$test/test-data ]; then \
 			echo "Running test $${test##*/}"; \
-			env -i QUIET=$$QUIET $${TERM:+"TERM=$$TERM"} $(ZSH) -f tests/test-highlighting.zsh "$${test##*/}"; \
+			env -i QUIET=$$QUIET $${TERM:+"TERM=$$TERM"} ZSH=${ZSH} $(ZSH) -f tests/test-highlighting.zsh "$${test##*/}"; \
 			: $$(( result |= $$? )); \
 		fi \
 	done; \

tests/test-highlighting.zsh

@@ -28,7 +28,6 @@
 # vim: ft=zsh sw=2 ts=2 et
 # -------------------------------------------------------------------------------------------------
 
-
 setopt NO_UNSET WARN_CREATE_GLOBAL
 
 # Required for add-zle-hook-widget.
@@ -72,8 +71,8 @@ fi
 
 # Load the main script.
 # While here, test that it doesn't eat aliases.
-print > >($results_filter | $root/tests/tap-colorizer.zsh) -r -- "# global (driver) tests"
-print > >($results_filter | $root/tests/tap-colorizer.zsh) -r -- "1..1"
+print > >($results_filter | $ZSH $root/tests/tap-colorizer.zsh) -r -- "# global (driver) tests"
+print > >($results_filter | $ZSH $root/tests/tap-colorizer.zsh) -r -- "1..1"
 alias -- +plus=plus
 alias -- _other=other
 local original_alias_dash_L_output="$(alias -L)"
@@ -83,7 +82,7 @@ if [[ $original_alias_dash_L_output == $(alias -L) ]]; then
 else
   print -r -- "not ok 1 # 'alias -- +foo=bar' is preserved"
   exit 1
-fi > >($results_filter | $root/tests/tap-colorizer.zsh)
+fi > >($results_filter | $ZSH $root/tests/tap-colorizer.zsh)
 
 # Overwrite _zsh_highlight_add_highlight so we get the key itself instead of the style
 _zsh_highlight_add_highlight()
@@ -283,7 +282,7 @@ integer something_failed=0
 ZSH_HIGHLIGHT_STYLES=()
 local data_file
 for data_file in $root/highlighters/$1/test-data/*.zsh; do
-  run_test "$data_file" | tee >($results_filter | $root/tests/tap-colorizer.zsh) | grep -v '^not ok.*# TODO' | grep -Eq '^not ok|^ok.*# TODO' && (( something_failed=1 ))
+  run_test "$data_file" | tee >($results_filter | $ZSH $root/tests/tap-colorizer.zsh) | grep -v '^not ok.*# TODO' | grep -Eq '^not ok|^ok.*# TODO' && (( something_failed=1 ))
   (( $pipestatus[1] )) && exit 2
 done