Let tests find fish and associated binaries via $FISHDIR

The default is still "../test/root/bin/", but we now pass this
through,
so you *can* run

`FISHDIR=$PWD ../tests/test_driver.sh $PWD/../tests/test.fish`

cmake/Tests.cmake

@@ -103,7 +103,7 @@ foreach(CHECK ${FISH_CHECKS})
   get_filename_component(CHECK_NAME ${CHECK} NAME)
   get_filename_component(CHECK ${CHECK} NAME_WE)
   add_test(NAME ${CHECK_NAME}
-    COMMAND sh ${CMAKE_CURRENT_BINARY_DIR}/tests/test_driver.sh
+    COMMAND env FISHDIR=${CMAKE_CURRENT_BINARY_DIR}/ ${CMAKE_CURRENT_BINARY_DIR}/tests/test_driver.sh
                ${CMAKE_CURRENT_BINARY_DIR}/tests/test.fish ${CHECK}
     WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/tests
   )
@@ -116,7 +116,7 @@ FILE(GLOB PEXPECTS CONFIGURE_DEPENDS ${CMAKE_SOURCE_DIR}/tests/pexpects/*.py)
 foreach(PEXPECT ${PEXPECTS})
   get_filename_component(PEXPECT ${PEXPECT} NAME)
   add_test(NAME ${PEXPECT}
-    COMMAND sh ${CMAKE_CURRENT_BINARY_DIR}/tests/test_driver.sh
+    COMMAND env FISHDIR=${CMAKE_CURRENT_BINARY_DIR}/ ${CMAKE_CURRENT_BINARY_DIR}/tests/test_driver.sh
       ${CMAKE_CURRENT_BINARY_DIR}/tests/interactive.fish ${PEXPECT}
     WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/tests
   )

tests/interactive.fish

@@ -31,10 +31,12 @@ function test_pexpect_file
         set -lx TERM dumb
 
         # Help the script find the pexpect_helper module in our parent directory.
+        set -q FISHDIR
+        or set -l FISHDIR ../test/root/bin/
         set -lx --prepend PYTHONPATH (realpath $PWD)
-        set -lx fish ../test/root/bin/fish
-        set -lx fish_key_reader ../test/root/bin/fish_key_reader
-        set -lx fish_test_helper ../test/root/bin/fish_test_helper
+        set -lx fish $FISHDIR/fish
+        set -lx fish_key_reader $FISHDIR/fish_key_reader
+        set -lx fish_test_helper $FISHDIR/fish_test_helper
 
         # Note we require Python3.
         python3 $file

tests/test.fish

@@ -30,6 +30,9 @@ or begin
     exit 125
 end
 
+set -q FISHDIR
+or set -l FISHDIR ../test/root/bin
+
 # Test littlecheck files.
 set -l skipped 0
 set -l failed 0
@@ -40,9 +43,9 @@ if set -q files_to_test[1]
 
     $python -S littlecheck.py \
         --progress $force_color \
-        -s fish=../test/root/bin/fish \
-        -s fish_test_helper=../test/root/bin/fish_test_helper \
-        -s filter-control-sequences='../test/root/bin/fish ../tests/filter-control-sequences.fish' \
+        -s fish=$FISHDIR/fish \
+        -s fish_test_helper=$FISHDIR/fish_test_helper \
+        -s filter-control-sequences="$FISHDIR/fish ../tests/filter-control-sequences.fish" \
         $files_to_test
 
     set -l littlecheck_status $status

tests/test_driver.sh

@@ -1,3 +1,4 @@
+#!/bin/sh
 # vim: set ts=4 sw=4 tw=100 et:
 
 # POSIX sh test driver to reduce dependency on fish in tests.
@@ -12,9 +13,13 @@
 # Folks, this is why you should use fish!
 IFS="$(printf "\n\b")"
 
+# If CDPATH is set, `cd foo` will print the directory.
+unset CDPATH
+
 # The first argument is the path to the script to launch; all remaining arguments are forwarded to
 # the script.
-fish_script="$1"
+# Resolve the script now because we are going to `cd` later.
+fish_script="$(realpath $1)"
 shift 1
 script_args="${@}"
 # Prevent $@ from persisting to sourced commands
@@ -32,6 +37,9 @@ die() {
 TESTS_ROOT="$(cd $(dirname "$0") && pwd -P)"
 BUILD_ROOT="$(cd $(dirname "$TESTS_ROOT") && pwd -P)"
 
+test -n "$FISHDIR" && FISHDIR=$(realpath -- "$FISHDIR")
+fish="${FISHDIR:-${BUILD_ROOT}/test/root/bin}/fish"
+
 if ! test -z "$__fish_is_running_tests"; then
     echo "Recursive test invocation detected!" 1>&2
     exit 10
@@ -42,7 +50,7 @@ fi
 
 # These are used read-only so it's OK to symlink instead of copy
 rm -f "$XDG_CONFIG_HOME/fish/functions"
-ln -s "$PWD/test_functions" "$XDG_CONFIG_HOME/fish/functions" || die "Failed to symlink"
+ln -s "${TESTS_ROOT}/test_functions" "$XDG_CONFIG_HOME/fish/functions" || die "Failed to symlink"
 
 # Set the function path at startup, referencing the default fish functions and the test-specific
 # functions.
@@ -68,8 +76,13 @@ export FISH_FAST_FAIL
 # Run the test script, but don't exec so we can clean up after it succeeds/fails. Each test is
 # launched directly within its TMPDIR, so that the fish tests themselves do not need to refer to
 # TMPDIR (to ensure their output as displayed in case of failure by littlecheck is reproducible).
-(cd $TMPDIR && env HOME="$homedir" "${BUILD_ROOT}/test/root/bin/fish" \
-    --init-command "${fish_init_cmd}" "$fish_script" "$script_args")
+if test -n "$script_args"; then
+    (cd $TMPDIR && env HOME="$homedir" "$fish" \
+                       --init-command "${fish_init_cmd}" "$fish_script" "$script_args")
+else
+    (cd $TMPDIR && env HOME="$homedir" "$fish" \
+                       --init-command "${fish_init_cmd}" "$fish_script")
+fi
 test_status="$?"
 
 rm -rf "$homedir"