determine tensor shapes programmatically

[SauravMaheshkar]

If you explore the test suite, you will find that we have hard-coded the tensor shapes in multiple places, viz.

jflux/tests/test_math.py

Lines 47 to 52 in e307cf8

	B, H, L, D = (
	1,
	24,
	4336,
	128,
	)

Ideally, we can add a utility function in tests/utils.py that can determine the output shape.