Added tests for kron! for diagonal matrices (#53184)

Co-authored-by: Jishnu Bhattacharya <[email protected]>

Author: ShrutiRDalvi

stdlib/LinearAlgebra/test/diagonal.jl

@@ -1266,4 +1266,15 @@ end
     @test copy(Diagonal(1:5)) === Diagonal(1:5)
 end
 
+@testset "kron! for Diagonal" begin
+    a = Diagonal([2,2])
+    b = Diagonal([1,1])
+    c = Diagonal([0,0,0,0])
+    kron!(c,b,a)
+    @test c == Diagonal([2,2,2,2])
+    c=Diagonal(Vector{Float64}(undef, 4))
+    kron!(c,a,b)
+    @test c == Diagonal([2,2,2,2])
+end
+
 end # module TestDiagonal