private void setRegister(Address a, String regname, long value) throws Exception {
		ProgramContext context = program.getProgramContext();
		Register gp = context.getRegister(regname);
		context.setRegisterValue(a, a.add(12), new RegisterValue(gp, BigInteger.valueOf(value)));
	}
quick and dirty test of the ProgramContextImpl just to see
if the values are being set for specified address range.
The ProgramContextPlugin will be a more complete test
program, with a gui interface to specify the values and
select/highlight an address range.
Ghidra/Features/Base/src/test/java/ghidra/program/util/ConstantPropogationReferenceTest.java