fix and test undef matrix for MArray

[oscardssmith]

I can't believe that I thought I didn't need tests after the first time I wrote this. Now they pass.

[codecov[bot]]

Codecov Report

Merging #358 (6d4d997) into master (a260a8a) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #358   +/-   ##
=======================================
  Coverage   90.27%   90.27%           
=======================================
  Files           9        9           
  Lines        1337     1337           
=======================================
  Hits         1207     1207           
  Misses        130      130           

:mega: We’re building smart automated test selection to slash your CI/CD build times. Learn more

[chriselrod]

julia> using ArrayInterfaceCore

julia> using ArrayInterfaceStaticArraysCore
[ Info: Precompiling ArrayInterfaceStaticArraysCore [dd5226c6-a4d4-4bc7-8575-46859f9c95b9]
ERROR: LoadError: UndefVarError: undefmatrix not defined
Stacktrace:
 [1] getproperty(x::Module, f::Symbol)
   @ Base ./Base.jl:31
 [2] top-level scope
   @ ~/.julia/packages/ArrayInterfaceStaticArraysCore/DxGup/src/ArrayInterfaceStaticArraysCore.jl:6
 [3] include
   @ ./Base.jl:419 [inlined]
 [4] include_package_for_output(pkg::Base.PkgId, input::String, depot_path::Vector{String}, dl_load_path::Vector{String}, load_path::Vector{String}, concrete_deps::Vector{Pair{Base.PkgId, UInt64}}, source::Nothing)
   @ Base ./loading.jl:1554
 [5] top-level scope
   @ stdin:1
in expression starting at /home/chriselrod/.julia/packages/ArrayInterfaceStaticArraysCore/DxGup/src/ArrayInterfaceStaticArraysCore.jl:1
in expression starting at stdin:1
ERROR: Failed to precompile ArrayInterfaceStaticArraysCore [dd5226c6-a4d4-4bc7-8575-46859f9c95b9] to /home/chriselrod/.julia/compiled/v1.8/ArrayInterfaceStaticArraysCore/jl_0NObzS.
Stacktrace:
 [1] error(s::String)
   @ Base ./error.jl:35
 [2] compilecache(pkg::Base.PkgId, path::String, internal_stderr::IO, internal_stdout::IO, keep_loaded_modules::Bool)
   @ Base ./loading.jl:1707
 [3] compilecache
   @ ./loading.jl:1651 [inlined]
 [4] _require(pkg::Base.PkgId)
   @ Base ./loading.jl:1337
 [5] _require_prelocked(uuidkey::Base.PkgId)
   @ Base ./loading.jl:1200
 [6] macro expansion
   @ ./loading.jl:1180 [inlined]
 [7] macro expansion
   @ ./lock.jl:223 [inlined]
 [8] require(into::Module, mod::Symbol)
   @ Base ./loading.jl:1144