@Override
			public void modifyLatest(MergeProgram mergeProgram) throws Exception {
				mergeProgram.addExternalLocation(libname, label, null, SourceType.USER_DEFINED);

				Program program = mergeProgram.getProgram();
				ExternalManager externalManager = program.getExternalManager();
				assertTrue(externalManager.contains(libname));
				ExternalLocation externalLocation =
					externalManager.getUniqueExternalLocation(libname, label);
				assertNotNull(externalLocation);
				assertEquals(false, externalLocation.isFunction());

				assertEquals(libname + "::" + label, externalLocation.toString());
				assertNull(externalLocation.getAddress());
				assertTrue(externalLocation.getSource() == SourceType.USER_DEFINED);
			}
The external function merger only detects and merges source differences when a name
difference is being merged.
Ghidra/Features/Base/src/test.slow/java/ghidra/app/merge/listing/ExternalMergerAddTest.java