factor

 USING: fuel.xref kernel sequences tools.test ;
 IN: fuel.xref.tests
 { t } [
     "fuel" apropos-xref empty? not
 ] unit-test
 { t } [
     "fuel" vocab-xref length 2 =
 ] unit-test
 { { } } [
     "i-dont-exist!" callees-xref
 ] unit-test