tests: Move assert_fail function to tests/libtest.sh

This moves the assert_fail function definition which was defined
and called in tests/test-remote-headers.sh. Done in preparation
for use of the assert_fail function in other test files.

Closes: #1669
Approved by: jlebon

tests/libtest.sh

@@ -648,3 +648,12 @@ assert_not_ref () {
         fatal "rev-parse $2 unexpectedly succeeded!"
     fi
 }
+
+assert_fail () {
+  set +e
+  $@
+  if [ $? = 0 ] ; then
+    echo 1>&2 "$@ did not fail"; exit 1
+  fi
+  set -euo pipefail
+}

tests/test-remote-headers.sh

@@ -33,15 +33,6 @@ setup_fake_remote_repo1 "archive" "" \
   --expected-header baz=badger \
   --expected-header "User-Agent=libostree/$V dodo/2.15"
 
-assert_fail (){
-  set +e
-  $@
-  if [ $? = 0 ] ; then
-    echo 1>&2 "$@ did not fail"; exit 1
-  fi
-  set -euo pipefail
-}
-
 cd ${test_tmpdir}
 rm repo -rf
 mkdir repo