Add unified diff support for `luatest.assert_equals` #438

mandesero · 2025-11-25T16:51:34Z

This patch adds unified diff output for t.assert_equals() failures when the test suite is run with the --diff option, using a vendored Lua implementation of google/diff-match-patch (luatest/vendor/diff_match_patch.lua taken from ¹).

Closes #412

Here is the output for the example from the issue:

code

local t = require('luatest')

local g = t.group()

g.test_table_assertion = function()
    local a = {
      a = {
        ["a"] = 1,
        ["b"] = 2,
        ["c"] = 3,
      },
    }

    local b = {
      a = {
        ["a"] = 1,
        ["b"] = 5,
        ["c"] = 8,
      },
    }
    t.assert_equals(a, b, 'compare tables')
end

g.test_string_assertion = function()
    local a = [[
aaaaa
bbbbb
ccccc
]]
    local b = [[
aaaaa
ddddd
ccccc
]]

    t.assert_equals(a, b, 'compare multiline strings')
end

g.test_msgpack_assertion = function()
    local msgpack = require('msgpack')
    local a = {1, 2, 3}
    local b = {1, 4, 3}

    t.assert_equals(msgpack.encode(a), msgpack.encode(b), 'compare encoded msgpack')
end

Failed tests:
-------------

1) tmp.test_table_assertion
/home/ubuntu/luatest/test/tmp_test.lua:21: compare tables
expected: {a = {a = 1, b = 5, c = 8}}
actual: {a = {a = 1, b = 2, c = 3}}
diff:
@@ -1,32 +1,32 @@
 ---
 a:
-  b: 5
  a: 1
  c: 8
+  b: 2
  a: 1
  c: 3
 ...

2) tmp.test_string_assertion
/home/ubuntu/luatest/test/tmp_test.lua:36: compare multiline strings
expected:
"aaaaa\
ddddd\
ccccc\
"
actual:
"aaaaa\
bbbbb\
ccccc\
"
diff:
@@ -1,34 +1,34 @@
 --- |
  aaaaa
-  ddddd
+  bbbbb
   ccccc
 ...

3) tmp.test_msgpack_assertion
/home/ubuntu/luatest/test/tmp_test.lua:44: compare encoded msgpack
expected: "�\1\4\3"
actual: "�\1\2\3"
diff:
@@ -1,20 +1,20 @@
 ---
- 1
-- 4
+- 2
 - 3
 ...

https://github.com/google/diff-match-patch/blob/master/lua/diff_match_patch.lua ↩

ligurio

Max, thanks for the patch!
Please take a look on my comments.

ligurio · 2025-11-27T08:23:52Z

CHANGELOG.md

+- Added support for unified diff output in `t.assert_equals()` failure messages.
+  The diff is shown only when the test suite is run with the `--diff` option (gh-412).


This functionality does no break anything, I would enable it by default and remove the option at all. The most popular case (IMHO) is using luatest via build system (CMake/Makefile) and with the option disabled by default one should need to explicitly enable it in a build system.

BTW we can use unified diff only for values that can be serialized to YAML.

I would enable it by default and remove the option at all.

Okay, done.

ligurio · 2025-11-27T08:28:05Z

luatest/diff.lua

+local function url_unescape(s)
+    return s:gsub("%%(%x%x)", function(h)
+        return string.char(tonumber(h, 16))
+    end)
+end


Oh, no, do not invent your own unescape function for URI.
Just use uri.unescape(), ¹.

Footnotes

https://www.tarantool.io/en/doc/latest/reference/reference_lua/uri/#lua-function.uri.unescape ↩

ligurio · 2025-11-27T08:29:27Z

test/luaunit/error_msg_test.lua

+    local actual_tbl = {a = {a = 1, b = 2, c = 3}}
+    local expected_tbl = {a = {a = 1, b = 5, c = 8}}


These cases are trivial. Tables with userdata (use newproxy() to create a sample), cdata and custom Tarantool types (like decimal/varbinary) ¹ are more interesting.

Footnotes

https://www.tarantool.io/en/doc/latest/reference/internals/msgpack_extensions/ ↩

I added support for custom types: decimal, datetime, uuid, and varbinary. Please check the latest changes.

ligurio · 2025-11-27T08:30:51Z

luatest/diff.lua

+    end)
+end
+
+local function prettify_patch(patch_text)


The function deserves a comment with high-level description a function purposes.

ligurio · 2025-11-27T08:41:51Z

luatest/diff.lua

+    local ok, encoded = pcall(yaml.encode, value)
+    if ok then
+        return encoded
+    end


if it is not serializable to YAML then ...?

luatest/diff.lua

This patch adds unified diff output for `t.assert_equals()` failures when the test suite is run with the `--diff` option, using a vendored Lua implementation of google/diff-match-patch (`luatest/vendor/diff_match_patch.lua` taken from [^1]). Closes tarantool#412 [^1]: https://github.com/google/diff-match-patch/blob/master/lua/diff_match_patch.lua

ligurio · 2025-11-28T11:27:42Z

luatest/assertions.lua

+function M.private.set_diff_enabled(value)
+    diff_enabled = value and true or false
+end


Sseems this function is not needed anymore, right?
As I get right, diff_enabled logic in the test was needed when option for diff support was present.

I use this here to avoid editing old tests

luatest/test/luaunit/error_msg_test.lua

Lines 9 to 15 in 26138ab

g.before_all(function()

t.private.set_diff_enabled(false)

end)

g.after_all(function()

t.private.set_diff_enabled(true)

end)

mandesero force-pushed the gh-412-print-diff branch from 69c5c84 to fef0177 Compare November 25, 2025 17:07

ligurio requested changes Nov 27, 2025

View reviewed changes

mandesero force-pushed the gh-412-print-diff branch from fef0177 to 1d91b35 Compare November 27, 2025 23:04

mandesero force-pushed the gh-412-print-diff branch from 1d91b35 to 26138ab Compare November 27, 2025 23:20

mandesero requested a review from ligurio November 27, 2025 23:23

ligurio reviewed Nov 28, 2025

View reviewed changes

mandesero requested a review from ligurio December 1, 2025 07:52

		- Added support for unified diff output in `t.assert_equals()` failure messages.
		The diff is shown only when the test suite is run with the `--diff` option (gh-412).

		local actual_tbl = {a = {a = 1, b = 2, c = 3}}
		local expected_tbl = {a = {a = 1, b = 5, c = 8}}

	g.before_all(function()
	t.private.set_diff_enabled(false)
	end)

	g.after_all(function()
	t.private.set_diff_enabled(true)
	end)

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Add unified diff support for `luatest.assert_equals` #438

Add unified diff support for `luatest.assert_equals` #438

mandesero commented Nov 25, 2025 •

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