test(basis): add runtests.jl

Test suite organizer for basis module.
Includes all basis function tests: partition of unity, derivatives,
interpolation, type stability, numerical accuracy, etc.

test/basis/runtests.jl

@@ -0,0 +1,14 @@
+# Test suite for basis functions module
+using Test
+
+@testset "Basis Functions" begin
+    include("test_partition_of_unity.jl")
+    include("test_svector_returns.jl")
+    include("test_derivatives.jl")
+    include("test_interpolation.jl")
+    include("test_all_elements.jl")
+    include("test_kronecker_delta.jl")
+    include("test_type_stability.jl")
+    include("test_numerical_accuracy.jl")
+    include("test_gradient_properties.jl")
+end