"expects valid input: schemas is a named list"
"expects valid input: schema elements correct lengths"
"expects valid input: schema elements contain characters of valid lengths"
"expects valid input: key attributes are in relation"
"orders key attributes with respect to order in attrs_order"
"orders attributes with respect to appearance in keys, then by attrs_order"
"is subsetted to a valid relation schema, follows usual subsetting rules..."
"expects a relation_schema value for subset re-assignment"
"^value must also be a relation_schema object$"
"is made unique to a valid relation schema"
"is composed of its attrs(), keys(), names(), and attrs_order()"
"is created with logical attribute classes"

relation_schema: concatenates without losing attribute orderings, if consistent

Falsifiable after 1 tests, and 100 shrinks
<simpleError in expect_all_true(mapply(identical, lapply(lst, attrs_order), lapply(lst,     function(x) intersect(attrs_order(res), attrs_order(x))))): could not find function "expect_all_true">
Counterexample:
[[1]]
0 relation schemas
0 attributes

[[2]]
0 relation schemas
2 attributes: b, d