Add tests

Author: mtfishman

test/test_basics.jl

@@ -1,5 +1,16 @@
 using ITensorBase:
-  ITensorBase, ITensor, Index, gettag, hastag, inds, plev, prime, settag, tags, unsettag
+  ITensorBase,
+  ITensor,
+  Index,
+  gettag,
+  hastag,
+  inds,
+  oneelement,
+  plev,
+  prime,
+  settag,
+  tags,
+  unsettag
 using DiagonalArrays: δ, delta, diagview
 using NamedDimsArrays: dename, name, named
 using Test: @test, @test_broken, @testset
@@ -35,6 +46,27 @@ using Test: @test, @test_broken, @testset
     @test plev(i) == 0
     @test length(tags(i)) == 0
   end
+  @testset "oneelement" begin
+    i = Index(3)
+    a = oneelement(i => 2)
+    @test a isa ITensor
+    @test ndims(a) == 1
+    @test issetequal(inds(a), (i,))
+    @test eltype(a) === Bool
+    @test a[1] == 0
+    @test a[2] == 1
+    @test a[3] == 0
+
+    i = Index(3)
+    a = oneelement(Float32, i => 2)
+    @test a isa ITensor
+    @test ndims(a) == 1
+    @test issetequal(inds(a), (i,))
+    @test eltype(a) === Float32
+    @test a[1] == 0
+    @test a[2] == 1
+    @test a[3] == 0
+  end
   @testset "delta" begin
     i, j = Index.((2, 2))
     for a in (