Stop importing Testing from ContainerTestSupport

Sources/ContainerTestSupport/BuildFixture.swift

@@ -18,7 +18,6 @@ import ContainerizationExtras
 import Darwin
 import Foundation
 import SystemPackage
-import Testing
 
 // MARK: - Build context types
 
@@ -309,12 +308,16 @@ extension ContainerFixture {
     /// Asserts that `path` exists as a regular file inside `container`.
     public func assertContainerHasFile(_ container: String, at path: String, _ comment: String? = nil) throws {
         let exists = try containerHasFile(container, at: path)
-        #expect(exists, "\(comment ?? path) should exist in container")
+        guard exists else {
+            throw CommandError.executionFailed("\(comment ?? path) should exist in container")
+        }
     }
 
     /// Asserts that `path` does NOT exist inside `container`.
     public func assertContainerMissingFile(_ container: String, at path: String, _ comment: String? = nil) throws {
         let exists = try containerHasFile(container, at: path)
-        #expect(!exists, "\(comment ?? path) should NOT exist in container")
+        guard !exists else {
+            throw CommandError.executionFailed("\(comment ?? path) should NOT exist in container")
+        }
     }
 }

Sources/ContainerTestSupport/ContainerFixture+ImageHelpers.swift

@@ -16,7 +16,6 @@
 
 import Foundation
 import SystemPackage
-import Testing
 
 // MARK: - Image inspect types
 
@@ -109,6 +108,8 @@ extension ContainerFixture {
     /// Asserts that the image was successfully built and is present in the image store.
     public func assertImageBuilt(_ image: String) throws {
         let name = try inspectImage(image)
-        #expect(name == image, "expected image \(image) to be present")
+        guard name == image else {
+            throw CommandError.executionFailed("expected image \(image) to be present")
+        }
     }
 }

Sources/ContainerTestSupport/ContainerFixture+MachineHelpers.swift

@@ -15,7 +15,6 @@
 //===----------------------------------------------------------------------===//
 
 import Foundation
-import Testing
 
 // MARK: - Machine output types
 

Sources/ContainerTestSupport/ContainerFixture.swift

@@ -20,7 +20,6 @@ import Foundation
 import Logging
 import Synchronization
 import SystemPackage
-import Testing
 
 /// Per-test fixture for CLI integration tests.
 ///