add concat() test for mutating inputs
add concat() test for mutating inputs

QuiverDart/quiver_pattern,googlearchive/quiver_async,googlearchive/quiver_optional,cbracken/quiver-dart,googlearchive/quiver_iterables,QuiverDart/quiver_hashcode,googlearchive/quiver_time,yjbanov/quiver_hashcode,QuiverDart/quiver_check,matgray/quiver_iterables,QuiverDart/quiver_time,QuiverDart/quiver_io,QuiverDart/quiver_collection,QuiverDart/quiver_strings,googlearchive/quiver_collection,googlearchive/quiver_hashcode,googlearchive/quiver_collection,QuiverDart/quiver_async,trinarytree/quiver-dart,EmmanuelOga/quiver-dart,QuiverDart/quiver_cache,EmmanuelOga/quiver-dart,googlearchive/quiver_hashcode,googlearchive/quiver_io,QuiverDart/quiver_optional,googlearchive/quiver_io,QuiverDart/quiver_io,alechenninger/quiver-dart,QuiverDart/quiver_optional,yjbanov/quiver_async,yjbanov/quiver_async,googlearchive/quiver_check,googlearchive/quiver_mirrors,willyp564/quiver-dart,QuiverDart/quiver_hashcode,googlearchive/quiver_strings,QuiverDart/quiver_iterables,googlearchive/quiver_pattern,trinarytree/quiver-dart,googlearchive/quiver_async,QuiverDart/quiver_iterables,QuiverDart/quiver_mirrors,googlearchive/quiver_strings,kevmoo/quiver-dart,kevmoo/quiver-dart,googlearchive/quiver_time,QuiverDart/quiver_async,QuiverDart/quiver_strings,googlearchive/quiver_check,yjbanov/quiver_hashcode,QuiverDart/quiver_mirrors,willyp564/quiver-dart,googlearchive/quiver_pattern,QuiverDart/quiver_time,googlearchive/quiver_optional,matgray/quiver_iterables,googlearchive/quiver_mirrors,jtmcdole/quiver-dart,QuiverDart/quiver_check,googlearchive/quiver_cache,googlearchive/quiver_iterables,QuiverDart/quiver_cache,cbracken/quiver-dart,QuiverDart/quiver_collection,googlearchive/quiver_cache,google/quiver-dart,jtmcdole/quiver-dart,QuiverDart/quiver_pattern,alechenninger/quiver-dart