fix up dense test

Author: ChrisRackauckas

test/nonsquare.jl

@@ -1,7 +1,19 @@
-using LinearSolve
+using LinearSolve, Test
 using SparseArrays, LinearAlgebra
 
 m, n = 13, 3
+
+A = rand(m, n); b = rand(m);
+prob = LinearProblem(A, b)
+res = A\b
+@test solve(prob).u ≈ res
+@test solve(prob, QRFactorization()) ≈ res
+@test solve(prob, KrylovJL_LSMR()) ≈ res
+
 A = sprand(m, n, 0.5); b = rand(m);
 prob = LinearProblem(A, b)
-solve(prob)
+res = A\b
+@test solve(prob).u ≈ res
+@test solve(prob, QRFactorization()) ≈ res
+@test solve(prob, KrylovJL_LSMR()) ≈ res
+