# Providing context to @test macro
**URL:** https://discourse.julialang.org/t/providing-context-to-test-macro/80235
**Category:** General Usage
**Created:** [April 29, 2022, 12:42am UTC](https://discourse.julialang.org/t/providing-context-to-test-macro/80235 "2022-04-29T00:42:02Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@col16](https://discourse.julialang.org/u/col16)
#### Post date: [April 29, 2022, 12:42am UTC](https://discourse.julialang.org/t/providing-context-to-test-macro/80235/1 "2022-04-29T00:42:02Z")
I’m using Julia to test the integrity of a large dataset by re-calculating values at random locations and checking that they match.
When a test that was run using the `@test` macro fails, it reports what was evaluated (and its stack trace), but I can’t work out how to provide additional context to those error messages—in my case, I’d like to report the location in the dataset that the error occurred.
Here’s a toy example to demonstrate this:
```julia
using Test
function foobar(n)
return n % 1000 == 0 ? true : false
end
@testset "Sample test" begin
for i = 1:10000
@test foobar(rand(1:1000)) == false
end
end
```
If I run the above it tells me that it fails some number of times. But the context in this example (analogous to the “location in the dataset”) would be the `i` value: what `i` value(s) did it fail at? Is there some way of being able to report this?
Thanks in advance! Cameron
---
### Author:  [@Sukera](https://discourse.julialang.org/u/Sukera)
#### Post date: [April 29, 2022, 3:10am UTC](https://discourse.julialang.org/t/providing-context-to-test-macro/80235/2 "2022-04-29T03:10:43Z")
You can put `@testset` on the loop directly and interpolate the loop variable into the description string:
```julia
@testset "Sample test $i" for i = 1:10000
@test foobar(rand(1:1000)) == false
end
```
Though I’d precompute the random numbers and use the resulting index in the description string as well, since that’s what actually makes the test fail. Maybe like `for i in rand(1:10000, 1000)`.
---
### Author:  [@col16](https://discourse.julialang.org/u/col16)
#### Post date: [April 29, 2022, 4:05am UTC](https://discourse.julialang.org/t/providing-context-to-test-macro/80235/3 "2022-04-29T04:05:33Z")
Thanks @Sukera. The problem is that I then end up with 10000 lines in my output:
```julia
Test Summary: | Pass Total
Sample test 1 | 1 1
Test Summary: | Pass Total
Sample test 2. | 1 1
Test Summary: | Pass Total
Sample test 3. | 1 1
```
…etc., until:
```julia
Test Summary: | Pass Total
Sample test 9999 | 1 1
Test Summary: | Pass Total
Sample test 10000 | 1 1
```
I would like run 10000 tests with the same name, BUT have the failure summaries tell me the `i` value that was used. Let’s take the following example:
```julia
Sample test: Test Failed at test_example.jl:9
Expression: foobar(rand(1:1000)) == false
Evaluated: true == false
(Stacktrace removed for brevity)
Test Summary: | Pass Fail Total
Sample test | 9993 7 10000
```
I’d like to be able to make the first line say
```julia
Sample test: Test Failed at test_example.jl:9 with i=2033
```
for example (spot the `i=2033` at the end). That way my console isn’t flooded with text; it only reports on actual failures.
---
### Author:  [@col16](https://discourse.julialang.org/u/col16)
#### Post date: [April 29, 2022, 4:40am UTC](https://discourse.julialang.org/t/providing-context-to-test-macro/80235/4 "2022-04-29T04:40:44Z")
I guess another approach would be to print the value `i` to the console and then overwrite it as I go, so that the terminal doesn’t get flooded—e.g. [https://discourse.julialang.org/t/how-clear-the-printed-content-in-terminal-and-print-to-the-same-line/](https://discourse.julialang.org/t/how-clear-the-printed-content-in-terminal-and-print-to-the-same-line/)
---
### Author:  [@Sukera](https://discourse.julialang.org/u/Sukera)
#### Post date: [April 29, 2022, 5:57am UTC](https://discourse.julialang.org/t/providing-context-to-test-macro/80235/5 "2022-04-29T05:57:17Z")
You can also nest `@testset` - that should only report failures. I do that for all my tests, with one big test set encompassing all smaller, more specific testsets.
---
### Author:  [@Sukera](https://discourse.julialang.org/u/Sukera)
#### Post date: [April 29, 2022, 10:09am UTC](https://discourse.julialang.org/t/providing-context-to-test-macro/80235/6 "2022-04-29T10:09:12Z")
For example:
```julia
using Random, Test
@testset "Nested example" begin
@testset "$i" for i in 1:10
@test rand(Xoshiro(i)) < 0.5
end
end
```
with output
> **Click me for result**
>
> ```julia
> 4: Test Failed at REPL[12]:3
> Expression: rand(Xoshiro(i)) < 0.5
> Evaluated: 0.8544835155398389 < 0.5
> Stacktrace:
> [1] macro expansion
> @ ~/julia/usr/share/julia/stdlib/v1.9/Test/src/Test.jl:464 [inlined]
> [2] macro expansion
> @ ./REPL[12]:3 [inlined]
> [3] macro expansion
> @ ~/julia/usr/share/julia/stdlib/v1.9/Test/src/Test.jl:1437 [inlined]
> [4] macro expansion
> @ ./REPL[12]:2 [inlined]
> [5] macro expansion
> @ ~/julia/usr/share/julia/stdlib/v1.9/Test/src/Test.jl:1360 [inlined]
> [6] top-level scope
> @ ./REPL[12]:2
> 5: Test Failed at REPL[12]:3
> Expression: rand(Xoshiro(i)) < 0.5
> Evaluated: 0.9776476808621083 < 0.5
> Stacktrace:
> [1] macro expansion
> @ ~/julia/usr/share/julia/stdlib/v1.9/Test/src/Test.jl:464 [inlined]
> [2] macro expansion
> @ ./REPL[12]:3 [inlined]
> [3] macro expansion
> @ ~/julia/usr/share/julia/stdlib/v1.9/Test/src/Test.jl:1437 [inlined]
> [4] macro expansion
> @ ./REPL[12]:2 [inlined]
> [5] macro expansion
> @ ~/julia/usr/share/julia/stdlib/v1.9/Test/src/Test.jl:1360 [inlined]
> [6] top-level scope
> @ ./REPL[12]:2
> 6: Test Failed at REPL[12]:3
> Expression: rand(Xoshiro(i)) < 0.5
> Evaluated: 0.8349918161453467 < 0.5
> Stacktrace:
> [1] macro expansion
> @ ~/julia/usr/share/julia/stdlib/v1.9/Test/src/Test.jl:464 [inlined]
> [2] macro expansion
> @ ./REPL[12]:3 [inlined]
> [3] macro expansion
> @ ~/julia/usr/share/julia/stdlib/v1.9/Test/src/Test.jl:1437 [inlined]
> [4] macro expansion
> @ ./REPL[12]:2 [inlined]
> [5] macro expansion
> @ ~/julia/usr/share/julia/stdlib/v1.9/Test/src/Test.jl:1360 [inlined]
> [6] top-level scope
> @ ./REPL[12]:2
> Test Summary: | Pass Fail Total Time
> Nested example | 7 3 10 0.0s
> 1 | 1 1 0.0s
> 2 | 1 1 0.0s
> 3 | 1 1 0.0s
> 4 | 1 1 0.0s
> 5 | 1 1 0.0s
> 6 | 1 1 0.0s
> 7 | 1 1 0.0s
> 8 | 1 1 0.0s
> 9 | 1 1 0.0s
> 10 | 1 1 0.0s
> ERROR: Some tests did not pass: 7 passed, 3 failed, 0 errored, 0 broken.
>
> ```
This still prints all elements on a failure in the summary, but to be honest I’m not sure having such a large loop resulting in individual tests is a good idea. Another approach could be to keep a list of ids that fail and only `@test` whether that list is empty:
```julia
julia> @testset "failing ids" begin
a = [1,2,43]
@test isempty(a)
end
failing ids: Test Failed at REPL[5]:3
Expression: isempty(a)
Evaluated: isempty([1, 2, 43])
Stacktrace:
[..] # omitted for brevity
Test Summary: | Fail Total Time
failing ids | 1 1 0.3s
ERROR: Some tests did not pass: 0 passed, 1 failed, 0 errored, 0 broken.
```
The upcoming 1.8 release will also allow [`@testset my_testset_function()`](https://github.com/JuliaLang/julia/pull/42518), which may be helpful for your grouping as well.
---
### Author:  [@col16](https://discourse.julialang.org/u/col16)
#### Post date: [April 29, 2022, 6:09pm UTC](https://discourse.julialang.org/t/providing-context-to-test-macro/80235/7 "2022-04-29T18:09:04Z")
Thanks @Sukera, that’s some things to think about. I’ll see whether I can make something work!