assert for function returning, nil/msg?

[jjvbsag]

Lua has a convention for functions to return nil and an error string in case of problems. Is there an assert for this? If not, how would you implement it?

Example:

    local ok,msg=output:set(-2)
    assertEquals("invalid value",msg)
    assertIsNil(ok)

I'd prefer something like

    assertNilMsg("invalid value",output:set(-2))

I tried by myself with

local function assertNilMsg(want,ok,msg)
    assertEquals(want,msg)
    assertIsNil(ok)
end

but in error case I get the wrong line in the test results

Failed tests:
-------------
1) TestLuaunitNilMsg.test3
/opt/unittest/luaunit-nil-msg.lua:17: expected: "good value"

Line 17 is my assertNilMsg and not the test case

[bluebird75]

Hi,

It's easy to write your own assert functions. Just look on how luaunit write them. For example, here the code for assertIsNil() 👍

function M.assertIsNil(value, extra_msg_or_nil)
    if value ~= nil then
        failure("expected: nil, actual: " ..prettystr(value), extra_msg_or_nil, 2)
    end
end

In your case, this should be something along the lines of :

local function assertNilMsg(want,ok,msg)
    if ok ~= nil or want ~= msg   then
        failure("Expected: nil with msg '"..want.."', got "..prettystr(ok).." with msg '"..msg.."'", nil, 2)
    end
end

A few advices : it is better to always show what you expected and what you actually got in the same message. The failure() function will take care of generating the proper error.

[jjvbsag]

Thank you. You code will throw an error, is msg is nil, so I changed it to

function M.assertNilMsg(want,ok,msg)
    if ok ~= nil or want ~= msg   then
        failure("Expected: nil with msg "..prettystr(want)..", got "..prettystr(ok).." with msg "..prettystr(msg), nil, 2)
    end
end

But thanks for the inspiration. Regards