tests/libtest.sh: Lift assert_jq from libvm.sh

We already had this logic, but it was in `libvm.sh`. Prep for using it
elsewhere.

Closes: #1766
Approved by: cgwalters

tests/common/libtest.sh

@@ -562,3 +562,16 @@ assert_files_hardlinked() {
         fatal "Files '$1' and '$2' are not hardlinked"
     fi
 }
+
+# $1  - json file
+# $2+ - assertions
+assert_jq() {
+    f=$1; shift
+    for expression in "$@"; do
+        if ! jq -e "${expression}" >/dev/null < $f; then
+            jq . < $f | sed -e 's/^/# /' >&2
+            echo 1>&2 "${expression} failed to match $f"
+            exit 1
+        fi
+    done
+}

tests/common/libvm.sh

@@ -354,15 +354,7 @@ vm_assert_layered_pkg() {
 # and asserts that they are true.
 vm_assert_status_jq() {
     vm_rpmostree status --json > status.json
-    vm_rpmostree status > status.txt
-    for expression in "$@"; do
-        if ! jq -e "${expression}" >/dev/null < status.json; then
-            jq . < status.json | sed -e 's/^/# /' >&2
-            echo 1>&2 "${expression} failed to match status.json"
-            cat status.txt
-            exit 1
-        fi
-    done
+    assert_jq status.json "$@"
 }
 
 vm_pending_is_staged() {