Test-Only Package Dependencies and Targets
- Proposal: SE-NNNN
- Authors: Harlan Haskins, Robert Widmann, thislooksfun
- Review Manager: TBD
- Status: Awaiting review
This proposal reinstates Swift Package Manager’s ability to fetch dependencies and build targets scoped exclusively to the testing module(s) of a given package.
Soon after SE-0019 identified the need for richer test-only dependencies and targets, a decision was made to remove the package manager’s fledgling ability to treat certain dependencies as test-only. This has led to a myriad of clever-but-needlessly-complex workarounds (, , ) on the part of 3rd parties to recover the feature themselves. In addition, the Swift community has come up with a number of their own frameworks to augment functionality in XCTest but depending on these external testing frameworks is brittle and difficult to get right.
We propose the re-introduction of the
testDependencies parameter in
Package Manifests to support external test-only dependencies. To support
local test-only targets we also propose the introduction of the
The behavior of the new
testDependencies parameter mirrors that of the
dependencies parameter with one important difference: fetched
dependencies are only built to support package-defined test targets as
part of an invocation of
import PackageDescription let package = Package( name: "Foo", targets: [ Target(name: "Foo") ], dependencies: [ .Package(url: "https://github.com/org/ana.git", versions: Version(1,0,0)...Version(1,9,9)), ], testDependencies: [ .Package(url: "https://github.com/org/anism.git", versions: Version(1,0,0)...Version(1,9,9)), ] )
Similarly, the behavior of the
testTargets field mirrors that of the
targets field but defines a set of targets that are only
built during an invocation of
swift test. Importantly, a target
testTargets may reference a target defined in
not vice-versa. Should that behavior be needed, the test target should
be promoted to a “full” target.
import PackageDescription let package = Package( name: "SwiftPM", targets: [ Target( name: "PackageDescription", dependencies: ), // MARK: Support libraries Target( /** Cross-platform access to bare `libc` functionality. */ name: "libc", dependencies: ), Target( /** “Swifty” POSIX functions from libc */ name: "POSIX", dependencies: ["libc"]), Target( /** Basic support library */ name: "Basic", dependencies: ["libc", "POSIX"]), /* Omitted for Brevity */ ], testTargets: [ Target( name: "BasicPerformanceTests", dependencies: ["Basic"]), /* Omitted for Brevity */ ] )
Impact on Existing Code
As this change is purely additive there will be no impact on existing code and no impact on existing packages.
Other names for the parameters to be added to the package manifest are possible.
The new support for executing specific tests could be exposed behind a flag.