@Test
	public void testGenerateChildren_ReadReference_NotCallInstruction_NoFunctionAtToAddress()
			throws Exception {

		//
		// Read reference to an instruction with a flow type that is not a call.  There is no 
		// function a the destination.
		//

		builder.addBytesFallthrough(firstCalledFunctionAddress);
		builder.disassemble(firstCalledFunctionAddress, 2);

		builder.createMemoryReference(firstCalledFunctionAddress, "0x1000", RefType.READ,
			SourceType.USER_DEFINED);
		List<GTreeNode> children = node1.generateChildren(TaskMonitor.DUMMY);
		assertTrue(children.isEmpty());
	}
This test class is covering the various types of 'calls' a function can make, such as a
direct call instruction, or through a user-defined reference.   External calls are also a bit
tricky.   This test was created by following the code paths in {@link OutgoingCallNode}
and making sure that each path was followed.
Ghidra/Features/Base/src/test.slow/java/ghidra/app/plugin/core/calltree/OutgoingCallNodeTest.java