Remove return which breaks testsets

[sdl1]

Closes #15

Gives correct behaviour in the following situation:

julia> results = @testset "test" begin
              test_interface(FakeTemplate{PointEstimate, SingleOutput}())
              @test false
           end
test: Test Failed at REPL[3]:3
  Expression: false
Stacktrace:
 [1] top-level scope at REPL[3]:3
 [2] top-level scope at /Users/julia/buildbot/worker/package_macos64/build/usr/share/julia/stdlib/v1.4/Test/src/Test.jl:1113
 [3] top-level scope at REPL[3]:2
Test Summary:                             | Pass  Fail  Total
test                                      |   13     1     14
  Models API Interface Test: FakeTemplate |   13           13
ERROR: Some tests did not pass: 13 passed, 1 failed, 0 errored, 0 broken.

julia> results.anynonpass
ERROR: UndefVarError: results not defined

[codecov]

Codecov Report

Merging #16 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master      #16   +/-   ##
=======================================
  Coverage   93.15%   93.15%           
=======================================
  Files           3        3           
  Lines          73       73           
=======================================
  Hits           68       68           
  Misses          5        5           

Impacted Files	Coverage Δ
src/test_utils.jl	92.53% <100.00%> (ø)

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[oxinabox]

docstring for test_interface says:

Returns the predictions of the Model`.

However, I checked all packages that i know of that use Models.jl
and none of them actually use this feature anymore.

I think should remove that docstring, and tag a breaking release.

Technically, you could rely on that feature right now, its just that your tests wouldn't work so great.

[sdl1]

Cool, I removed the docstring and changed the version to be breaking

[oxinabox]

Cool.
merge then register release.
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