Add a test-specific Project.toml to work around Pkg issue.

Project.toml

@@ -11,7 +11,6 @@ Preferences = "21216c6a-2e73-6563-6e65-726566657250"
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
 Scratch = "6c6a2e73-6563-6170-7368-637461726353"
 TOML = "fa267f1f-6049-4f14-aa54-33bafae1ed76"
-Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 UserNSSandbox_jll = "b88861f7-1d72-59dd-91e7-a8cc876a4984"
 
 [compat]

test/Project.toml

@@ -0,0 +1,8 @@
+# A bug in Julia 1.6.0's Pkg causes Preferences to be dropped during `Pkg.test()`, so we work around
+# it by explicitly creating a `test/Project.toml` which will correctly communicate any preferences
+# through to the child Julia process.  X-ref: https://github.com/JuliaLang/Pkg.jl/issues/2500
+
+[deps]
+Artifacts = "56f22d72-fd6d-98f1-02f0-08ddc0907c33"
+Scratch = "6c6a2e73-6563-6170-7368-637461726353"
+Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"

test/Sandbox.jl

@@ -7,7 +7,7 @@ if !success(`sudo -k -n true`)
     all_executors = filter(exe -> exe != PrivilegedUserNamespacesExecutor, all_executors)
 end
 
-rootfs_dir = artifact"AlpineRootfs"
+rootfs_dir = Sandbox.alpine_rootfs()
 for executor in all_executors
     if !executor_available(executor)
         @error("Skipping $(executor) tests, as it does not seem to be available")

test/SandboxConfig.jl

@@ -1,11 +1,11 @@
 using Test, Artifacts
 
 @testset "SandboxConfig" begin
-    rootfs_dir = artifact"AlpineRootfs"
+    rootfs_dir = Sandbox.alpine_rootfs()
 
     @testset "minimal config" begin
         config = SandboxConfig(Dict("/" => rootfs_dir))
-        
+
         @test haskey(config.read_only_maps, "/")
         @test config.read_only_maps["/"] == rootfs_dir
         @test isempty(config.read_write_maps)
@@ -59,4 +59,4 @@ using Test, Artifacts
         @test_throws ArgumentError SandboxConfig(Dict("/" => rootfs_dir); pwd="lib")
         @test_throws ArgumentError SandboxConfig(Dict("/" => rootfs_dir); entrypoint="init")
     end
-end
+end