'Module was not compiled for testing' when using @testable

This is probably because your main target `Enable Testability` is set to `NO`. You should set it to `YES` in the debug scheme (which is used for running your tests).

If you use Carthage, this problem can be caused by importing frameworks with `@testable`, because they are built with a release scheme.

Most of the times it's bad practice to import frameworks with that prefix, so you could avoid it.
If you can't, you should `Enable Testability` in the frameworks' release scheme.

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In your main target you need to set the `Enable Testability` build option to Yes.

As per the comment by @earnshavian below, this should only be used on debug builds as per apple release notes: "The Enable Testability build setting should be used only in your Debug configuration, because it prohibits optimizations that depend on not exporting internal symbols from the app or framework"

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This didn't occur in my projects prior to Xcode 8, but after I upgraded to Xcode 8, it made me perplexed.

The answers posted here didn't get my problems resolved. For me, I just ditched these tests as it is not needed. So uncheck the test buttons:

[![enter image description here][1]][1]
And now the error has gone out.


[1]: