[SR-1351] Add a way to run swift-test on a fixture in tests

[swift-ci]

Previous ID	SR-1351
Radar	None
Original Reporter	czechboy0 (JIRA User)
Type	Bug

Additional Detail from JIRA

Votes	0
Component/s	Package Manager
Labels	Bug
Assignee	@ddunbar
Priority	Medium

md5: 725492ca9c4d45e17807b793a4cfc46f

Issue Description:

Currently SwiftPM tests can verify that a fixture can build in SwiftPM, but no that it can test. To avoid swift-test specific bugs for certain layouts, we should add a way to run swift-test on a fixture. See discussion here: #282 (comment)

[ddunbar]

See:
#143 (comment)
for more context.

[ddunbar]

I started looking at this again last night.

I was hoping that we could extend the "fake toolchain" concept we use in the bootstrap script to just also support Foundation and XCTest. However, it turns out this doesn't work. The problem is that the Swift compiler will find its resources relative to the realpath of itself, and so it wants to find them in the swift build directory.

At the same time, I am investigating: https://bugs.swift.org/browse/SR-1631 which is annoying because I need to investigate with a built toolchain which the normal development process doesn't have.

The combination of the two of these is making me want to push more on my "toolchain based build process" ideas...