Add unit tests for normalisation

[dschwoerer]

No description provided.

[ZedThree]

Please could you add a comment explaining why we don't want to reset the jacobian in this case? I guess this is something to do with not wanting to recalculate the slices? But if we're calling this, then we've changed the metric, so how do we ensure the jacobian is in sync with the metric?

Also we can collapse the if statements into one :)

[dschwoerer]

Please could you add a comment explaining why we don't want to reset the jacobian in this case? I guess this is something to do with not wanting to recalculate the slices?

Exactly. We could do this, but it is rather bothersome.

But if we're calling this, then we've changed the metric, so how do we ensure the jacobian is in sync with the metric?

We hope the user knows what they are doing. We also have no check that co and contra variant tensor are aligned. We could add a CHECK > 2 check to ensure J is somewhat consistent (and maybe co and contravariant tensors, too)

[ZedThree]

Oh, is the actual problem just the ordering of calls?

BOUT-dev/src/mesh/coordinates.cxx

Lines 1284 to 1286 in 61ca9f1

	setJ(J);
	setBxy(Bxy);
	invalidateMetricCaches();

BOUT-dev/src/mesh/coordinates.cxx

Lines 1314 to 1337 in 61ca9f1

	if (norm.J.has_value()) {
	if (J().hasParallelSlices()) {
	setJ(FieldMetricParallel{J() / *norm.J});
	} else {
	setJ(J() / *norm.J);
	}
	}
	if (norm.Bxy.has_value()) {
	if (Bxy().hasParallelSlices()) {
	setBxy(FieldMetricParallel{Bxy() / *norm.Bxy});
	} else {
	setBxy(Bxy() / *norm.Bxy);
	}
	}
	if (norm.dx.has_value()) {
	setDx(dx() / *norm.dx);
	}
	if (norm.dy.has_value()) {
	setDy(dy() / *norm.dy);
	}
	if (norm.dz.has_value()) {
	setDz(dz() / *norm.dz);
	}
	invalidateMetricCaches();

Should we just move the call to invalidateMetricCaches() to before calling setJ?