Provide test only feature in Test target

test-target.swift

protocol ProductionFeatureProtocol: TestFeature1, TestFeature2 {

}

struct DefaultProductionFeature: ProductionFeatureProtocol {

}

protocol TestFeature1 {
	func testOnly1()
}

extension TestFeature1 {
	func testOnly1() {
		print("Default test feature1")
	}
}

protocol TestFeature2 {
	func testOnly2()
}

extension TestFeature2 {
	func testOnly2() {
		print("Default test feature2")
	}
}

let feature = DefaultProductionFeature()
feature.testOnly1()
feature.testOnly2()

extension DefaultProductionFeature {
	func testOnly1() {
		print("Overrided test feature1")
	}
	func testOnly2() {
		print("Overrided test feature2")
	}
}

The problem of this approach is that extension DefaultProductionFeature cannot be declared in another module, i.e. Test target.

The reason is that when a module is compiled, its context has been resolved already, and cannot be altered from outside. Read more