Fixes #37. Replacing existing priority

test/tc_priority.vim

@@ -0,0 +1,28 @@
+let s:here = expand('<sfile>:p:h')
+let s:context = todo#txt#__context__()
+let s:context['data'] = s:here . '/tc_priority.todo.txt'
+let s:tc = unittest#testcase#new('Priority', s:context)
+
+let s:TODAY = strftime("%Y-%m-%d")
+
+let s:PRIORITY_INSERTED = [
+      \ '(A) example task',
+      \ ]
+
+let s:PRIORITY_REPLACED = [
+      \ '(C) example task',
+      \ ]
+
+function! s:tc.test_insert_priority()
+  call self.data.goto('insert_priority')
+  call todo#txt#prioritize_add('A')
+  call self.assert_equal(s:PRIORITY_INSERTED, self.data.get('insert_priority'))
+endfunction
+
+function! s:tc.test_replace_priority()
+  call self.data.goto('replace_priority')
+  call todo#txt#prioritize_add('C')
+  call self.assert_equal(s:PRIORITY_REPLACED, self.data.get('replace_priority'))
+endfunction
+
+unlet s:tc