# How can I get useful diff messeges when comparing tuples?
**URL:** https://discourse.julialang.org/t/how-can-i-get-useful-diff-messeges-when-comparing-tuples/57709
**Category:** New to Julia
**Tags:** testing
**Created:** [March 22, 2021, 1:03pm UTC](https://discourse.julialang.org/t/how-can-i-get-useful-diff-messeges-when-comparing-tuples/57709 "2021-03-22T13:03:18Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@justinsgray](https://discourse.julialang.org/u/justinsgray)
#### Post date: [March 22, 2021, 1:03pm UTC](https://discourse.julialang.org/t/how-can-i-get-useful-diff-messeges-when-comparing-tuples/57709/1 "2021-03-22T13:03:18Z")
Im just spooling up with Julia, and Im having difficulty getting useful diff-msgs on some of the tests I am writing, when using ExtendedTestSet. The problem seems to be related to the type of vectors/tuples i am comparing. Sometimes I can get a diff, othertimes I get nothing!
I think the problem is that there is not a diff function defined for the types I am trying to compare, but I am unsure how to define one.
How can I make my own diff methods, and structure my own output for them?
Here is a simple example:
```julia
using Test
using TestSetExtensions
@testset ExtendedTestSet "unit test for inside_ranges" begin
# not useful diff msg
@test (2,3) == (3,4)
# sort of useful diff msg
@test [2,3] == [3,4]
end
```
gives:
```julia
=====================================================
unit test for inside_ranges: **Test Failed**
Expression: (2, 3) == (3, 4)
Diff:
nothing
=====================================================
=====================================================
unit test for inside_ranges: **Test Failed**
Expression: [2, 3] == [3, 4]
Diff:
[2, 3, 4]
=====================================================
```
---
### Author:  [@lmiq](https://discourse.julialang.org/u/lmiq)
#### Post date: [March 22, 2021, 1:13pm UTC](https://discourse.julialang.org/t/how-can-i-get-useful-diff-messeges-when-comparing-tuples/57709/2 "2021-03-22T13:13:14Z")
If you broadcast the comparison, i. e. `(2,3) .== (3,4)` you get:
```julia
Expression evaluated to non-Boolean
Expression: (2, 3) .== (3, 4)
Value: (false, false)
```
Or you can get the same error message you get with arrays converting the tuples into arrays:
```julia
@test [(2,3)...] == [(3,4)...]
```
---
### Author:  [@justinsgray](https://discourse.julialang.org/u/justinsgray)
#### Post date: [March 22, 2021, 1:18pm UTC](https://discourse.julialang.org/t/how-can-i-get-useful-diff-messeges-when-comparing-tuples/57709/3 "2021-03-22T13:18:43Z")
Thanks. Thats helpful. I’d still like to code my own diff though. Is it possible to do that?
---
### Author:  [@lmiq](https://discourse.julialang.org/u/lmiq)
#### Post date: [March 22, 2021, 1:34pm UTC](https://discourse.julialang.org/t/how-can-i-get-useful-diff-messeges-when-comparing-tuples/57709/4 "2021-03-22T13:34:58Z")
Probably you can, you should check how to do that in the documentation of `TestSetExtensions`. What you certainly can is define your own function to compare tuples, like, for instance:
```julia
julia> function diff_tuple(x,y)
diff = Tuple[]
for i in eachindex(x)
if x[i] != y[i]
push!(diff,((i,x[i]=>y[i])))
end
end
if length(diff) == 0
return true
end
return diff
end
diff_tuple (generic function with 1 method)
julia> @test diff_tuple((2,3),(2,3))
Test Passed
julia> @test diff_tuple((2,3),(3,4))
Error During Test at REPL[65]:1
Expression evaluated to non-Boolean
Expression: diff_tuple((2, 3), (3, 4))
Value: Tuple[(1, 2 => 3), (2, 3 => 4)]
```
The error message here indicates which elements changed, at which position, and from what to what.
Edit: It didn’t seem to me that the package was written to be really extendable. An inner change was needed. I have added a pull request here in which the tuples are expanded into vectors and the error message is printed as such:
> **[Comparing ssfrr:master...lmiq:patch-1 · ssfrr/TestSetExtensions.jl](https://github.com/ssfrr/TestSetExtensions.jl/compare/master...lmiq:patch-1)**
>
> Extensions to Julia's Base.Test. Contribute to ssfrr/TestSetExtensions.jl development by creating an account on GitHub.
Not very elegant, but better than printing `nothing`.