Problem: Only some assert functions can be used as a method.
Solution: Allow using most assert functions as a method.
24278d2407
Port tests to assert_spec.lua.
Problem: More functions can be used as a method.
Solution: Add append(), appendbufline(), assert_equal(), etc.
Also add the :eval command.
25e42231d3
:eval is already ported.
Problem: The eval.txt help file is too big.
Solution: Split off testing support to testing.txt. Move function details
to where the functionality is explained.
ed997adaa1
Vim commit 5477506a9f01d40fad2e8f0555bc37adee30478f
contains the duplicate tag fix in runtime/doc/testing.txt.
