Eliminate shared temporary directory for tests

Aside from the fact that the shared state could cause problems, tests
were randomly assuming it would be created where that wasn't the case.
In particular, `redirect.fish` and `basic.fish` were failing on only
macOS because `../test/temp` didn't exist yet - it would be created by
other tests later.

tests/checks/basic.fish

@@ -42,12 +42,12 @@ end
 # Simple function tests
 
 function foo
-    echo >../test/temp/fish_foo.txt $argv
+    echo >$TMPDIR/fish_foo.txt $argv
 end
 
 foo hello
 
-cat ../test/temp/fish_foo.txt |read foo
+cat $TMPDIR/fish_foo.txt |read foo
 
 if test $foo = hello;
   echo Test 2 pass
@@ -297,7 +297,7 @@ else if test -n "def"
 else if not_a_valid_command but it should be OK because a previous branch was taken
 	echo "epsilon 5.3"
 else if test ! -n "abc"
-	echo "epsilon 5.4"	
+	echo "epsilon 5.4"
 end
 #CHECK: epsilon5.2
 
@@ -327,10 +327,10 @@ type -q -f fish_test_type_zzz ; echo $status
 
 # ensure that builtins that produce no output can still truncate files
 # (bug PCA almost reintroduced!)
-echo abc > ../test/temp/file_truncation_test.txt
-cat ../test/temp/file_truncation_test.txt
-echo -n > ../test/temp/file_truncation_test.txt
-cat ../test/temp/file_truncation_test.txt
+echo abc > $TMPDIR/file_truncation_test.txt
+cat $TMPDIR/file_truncation_test.txt
+echo -n > $TMPDIR/file_truncation_test.txt
+cat $TMPDIR/file_truncation_test.txt
 #CHECK: abc
 
 # Test events.

tests/checks/redirect.fish

@@ -67,8 +67,8 @@ rm -Rf $tmpdir
 begin
     echo output
     echo errput 1>&2
-end 2>&1 | sort | tee ../test/temp/tee_test.txt
-cat ../test/temp/tee_test.txt
+end 2>&1 | sort | tee $TMPDIR/tee_test.txt
+cat $TMPDIR/tee_test.txt
 #CHECK: errput
 #CHECK: output
 #CHECK: errput

tests/checks/wildcard.fish

@@ -16,16 +16,15 @@ cd $oldpwd
 rm -Rf $dir
 
 
-# Verify that we can do wildcard expansion when we
-# don't have read access to some path components
+# Verify that we can do wildcard expansion when we don't have read access to some path components.
 # See #2099
-set -l where ../test/temp/fish_wildcard_permissions_test/noaccess/yesaccess
+set -l where $TMPDIR/fish_wildcard_permissions_test/noaccess/yesaccess
 mkdir -p $where
 chmod 300 (dirname $where) # no read permissions
 mkdir -p $where
 # "__env.fish" here to confirm ordering - #6593.
 touch $where/alpha.txt $where/beta.txt $where/delta.txt $where/__env.fish
-echo $where/*
-#CHECK: ../test/temp/fish_wildcard_permissions_test/noaccess/yesaccess/__env.fish ../test/temp/fish_wildcard_permissions_test/noaccess/yesaccess/alpha.txt ../test/temp/fish_wildcard_permissions_test/noaccess/yesaccess/beta.txt ../test/temp/fish_wildcard_permissions_test/noaccess/yesaccess/delta.txt
+echo $where/* | string replace -a $TMPDIR '$TMPDIR'
+#CHECK: $TMPDIR/fish_wildcard_permissions_test/noaccess/yesaccess/__env.fish $TMPDIR/fish_wildcard_permissions_test/noaccess/yesaccess/alpha.txt $TMPDIR/fish_wildcard_permissions_test/noaccess/yesaccess/beta.txt $TMPDIR/fish_wildcard_permissions_test/noaccess/yesaccess/delta.txt
 chmod 700 (dirname $where) # so we can delete it
-rm -rf ../test/temp/fish_wildcard_permissions_test
+rm -rf $TMPDIR/fish_wildcard_permissions_test

tests/test_driver.sh

@@ -54,6 +54,12 @@ XDG_RUNTIME_DIR="$homedir/xdg_runtime_dir"
 export XDG_CONFIG_HOME
 mkdir -p $XDG_RUNTIME_DIR/fish || die
 
+# Create a temp/scratch directory for tests to use, if they want (tests shouldn't write to a
+# shared temp folder).
+TMPDIR="$homedir/temp"
+mkdir ${TMPDIR}
+export TMPDIR
+
 # These are used read-only so it's OK to symlink instead of copy
 rm -f "$XDG_CONFIG_HOME/fish/functions"
 ln -s "$PWD/test_functions" "$XDG_CONFIG_HOME/fish/functions" || die "Failed to symlink"