I can't seem to be able to set up dub so that I can build subpackages.

Do I have a mistake in the json configs?

What I have:

./dub.json:

{
	"name": "test",
	"authors": [
		"timoses"
	],
	"description": "A minimal D application.",
	"copyright": "Copyright © 2018, timoses",
	"license": "proprietary",

    "dependencies": {
        "test:dep"
    },

    "subPackages": [
        "dep",
        "dep2"
    ]
}

./dep/dub.json:

{
	"name": "dep",
	"authors": [
		"timoses"
	],
	"description": "A minimal D application.",
	"copyright": "Copyright © 2018, timoses",
	"license": "proprietary",

    "dependencies": {
        "test:dep2": "*"
    },

    "targetType": "library"
}

./dep2/dub.json:

{
	"name": "dep2",
	"authors": [
		"timoses"
	],
	"description": "A minimal D application.",
	"copyright": "Copyright © 2018, timoses",
	"license": "proprietary"
}

dub upgrade --vverbose yields (dub v1.6.0, though error is same for v1.7.2):

Using dub registry url 'http://code.dlang.org/'
Refreshing local packages (refresh existing: true)...
Looking for local package map at /var/lib/dub/packages/local-packages.json
Looking for local package map at /home/timoses/.dub/packages/local-packages.json
iterating dir /home/timoses/.dub/packages/
iterating dir /home/timoses/.dub/packages/ entry eventcore-0.8.29
iterating dir /home/timoses/.dub/packages/ entry vibe-d-0.8.3-rc.1
iterating dir /home/timoses/.dub/packages/ entry eventcore-0.8.28
iterating dir /home/timoses/.dub/packages/ entry diet-ng-1.4.3
iterating dir /home/timoses/.dub/packages/ entry stdx-allocator-2.77.0
iterating dir /home/timoses/.dub/packages/ entry arsd-official-1.2.2
iterating dir /home/timoses/.dub/packages/ entry diet-ng-1.4.4
iterating dir /home/timoses/.dub/packages/ entry vibe-core-1.0.0
iterating dir /home/timoses/.dub/packages/ entry botan-math-1.0.3
iterating dir /home/timoses/.dub/packages/ entry vibe-core-1.3.0
iterating dir /home/timoses/.dub/packages/ entry eventcore-0.8.27
iterating dir /home/timoses/.dub/packages/ entry libasync-0.8.3
iterating dir /home/timoses/.dub/packages/ entry dstep-0.2.3
iterating dir /home/timoses/.dub/packages/ entry htmld-0.3.1
iterating dir /home/timoses/.dub/packages/ entry memutils-0.4.10
iterating dir /home/timoses/.dub/packages/ entry taggedalgebraic-0.10.7
iterating dir /home/timoses/.dub/packages/ entry diet-ng-1.2.1
iterating dir /home/timoses/.dub/packages/ entry openssl-1.1.5_1.0.1g
iterating dir /home/timoses/.dub/packages/ entry vibe-d-0.7.31
iterating dir /home/timoses/.dub/packages/ entry vibe-d-0.8.3-alpha.4
iterating dir /home/timoses/.dub/packages/ entry memutils-0.4.9
iterating dir /home/timoses/.dub/packages/ entry vibe-d-0.8.2-rc.1
iterating dir /home/timoses/.dub/packages/ entry libdominator-1.1.6
iterating dir /home/timoses/.dub/packages/ entry kxml
Determined package version using GIT: kxml 1.0.1+commit.1.g337ff04
iterating dir /home/timoses/.dub/packages/ entry libevent-2.0.2_2.0.16
iterating dir /home/timoses/.dub/packages/ entry vibe-d-0.8.3-alpha.2
iterating dir /home/timoses/.dub/packages/ entry kxml-1.0.1
iterating dir /home/timoses/.dub/packages/ entry vibe-core-1.4.0-alpha.1
iterating dir /home/timoses/.dub/packages/ entry vibe-d-0.8.2
iterating dir /home/timoses/.dub/packages/ entry vibe-core-1.4.0-rc.1
iterating dir /home/timoses/.dub/packages/ entry vibe-d-0.7.32
iterating dir /home/timoses/.dub/packages/ entry vibe-core-1.3.0-rc.2
iterating dir /home/timoses/.dub/packages/ entry mysql-native-1.1.2
iterating dir /home/timoses/.dub/packages/ entry dproto-1.3.2
iterating dir /home/timoses/.dub/packages/ entry taggedalgebraic-0.10.9
iterating dir /home/timoses/.dub/packages/ entry openssl-1.1.6_1.0.1g
iterating dir /home/timoses/.dub/packages/ entry eventcore-0.8.25
iterating dir /home/timoses/.dub/packages/ entry botan-1.12.9
Note: Failed to determine version of package dep at .. Assuming ~master.
Refreshing local packages (refresh existing: false)...
Looking for local package map at /var/lib/dub/packages/local-packages.json
Looking for local package map at /home/timoses/.dub/packages/local-packages.json
iterating dir /home/timoses/.dub/packages/
iterating dir /home/timoses/.dub/packages/ entry eventcore-0.8.29
iterating dir /home/timoses/.dub/packages/ entry vibe-d-0.8.3-rc.1
iterating dir /home/timoses/.dub/packages/ entry eventcore-0.8.28
iterating dir /home/timoses/.dub/packages/ entry diet-ng-1.4.3
iterating dir /home/timoses/.dub/packages/ entry stdx-allocator-2.77.0
iterating dir /home/timoses/.dub/packages/ entry arsd-official-1.2.2
iterating dir /home/timoses/.dub/packages/ entry diet-ng-1.4.4
iterating dir /home/timoses/.dub/packages/ entry vibe-core-1.0.0
iterating dir /home/timoses/.dub/packages/ entry botan-math-1.0.3
iterating dir /home/timoses/.dub/packages/ entry vibe-core-1.3.0
iterating dir /home/timoses/.dub/packages/ entry eventcore-0.8.27
iterating dir /home/timoses/.dub/packages/ entry libasync-0.8.3
iterating dir /home/timoses/.dub/packages/ entry dstep-0.2.3
iterating dir /home/timoses/.dub/packages/ entry htmld-0.3.1
iterating dir /home/timoses/.dub/packages/ entry memutils-0.4.10
iterating dir /home/timoses/.dub/packages/ entry taggedalgebraic-0.10.7
iterating dir /home/timoses/.dub/packages/ entry diet-ng-1.2.1
iterating dir /home/timoses/.dub/packages/ entry openssl-1.1.5_1.0.1g
iterating dir /home/timoses/.dub/packages/ entry vibe-d-0.7.31
iterating dir /home/timoses/.dub/packages/ entry vibe-d-0.8.3-alpha.4
iterating dir /home/timoses/.dub/packages/ entry memutils-0.4.9
iterating dir /home/timoses/.dub/packages/ entry vibe-d-0.8.2-rc.1
iterating dir /home/timoses/.dub/packages/ entry libdominator-1.1.6
iterating dir /home/timoses/.dub/packages/ entry kxml
iterating dir /home/timoses/.dub/packages/ entry libevent-2.0.2_2.0.16
iterating dir /home/timoses/.dub/packages/ entry vibe-d-0.8.3-alpha.2
iterating dir /home/timoses/.dub/packages/ entry kxml-1.0.1
iterating dir /home/timoses/.dub/packages/ entry vibe-core-1.4.0-alpha.1
iterating dir /home/timoses/.dub/packages/ entry vibe-d-0.8.2
iterating dir /home/timoses/.dub/packages/ entry vibe-core-1.4.0-rc.1
iterating dir /home/timoses/.dub/packages/ entry vibe-d-0.7.32
iterating dir /home/timoses/.dub/packages/ entry vibe-core-1.3.0-rc.2
iterating dir /home/timoses/.dub/packages/ entry mysql-native-1.1.2
iterating dir /home/timoses/.dub/packages/ entry dproto-1.3.2
iterating dir /home/timoses/.dub/packages/ entry taggedalgebraic-0.10.9
iterating dir /home/timoses/.dub/packages/ entry openssl-1.1.6_1.0.1g
iterating dir /home/timoses/.dub/packages/ entry eventcore-0.8.25
iterating dir /home/timoses/.dub/packages/ entry botan-1.12.9
Collecting dependencies for dep
  Version selection for dependency test (test) of dep is missing.
  Missing dependency test >=0.0.0 of dep
Upgrading project in /media/sf_C_DRIVE/Users/funke_t1/Code/test/dep
Search for versions of test (1 package suppliers)
Downloading metadata for test
Getting from http://code.dlang.org/packages/test.json
Getting http://code.dlang.org/packages/test.json...
Package test not found at registry at http://code.dlang.org/ (404): HTTP request returned status code 404 (Not Found)
No versions for test for registry at http://code.dlang.org/ (fallback registry at https://code-mirror.dlang.io/)
Nothing found for test
Configurations used for dependency resolution:
  test (0, required): [invalid]
Root package dep references unknown package test
Full exception: object.Exception@source/dub/dependencyresolver.d(159): Root package dep references unknown package test
----------------
source/dub/dependencyresolver.d:159 long dub.dependencyresolver.DependencyResolver!(dub.dependency.Dependency, dub.dependency.Dependency).DependencyResolver.resolve(dub.dependencyresolver.DependencyResolver!(dub.dependency.Dependency, dub.dependency.Dependency).DependencyResolver.TreeNode, bool).validateConfigs(dub.dependencyresolver.DependencyResolver!(dub.dependency.Dependency, dub.dependency.Dependency).DependencyResolver.TreeNode, ref immutable(char)[]) [0x88b7bb]
source/dub/dependencyresolver.d:205 dub.dependency.Dependency[immutable(char)[]] dub.dependencyresolver.DependencyResolver!(dub.dependency.Dependency, dub.dependency.Dependency).DependencyResolver.resolve(dub.dependencyresolver.DependencyResolver!(dub.dependency.Dependency, dub.dependency.Dependency).DependencyResolver.TreeNode, bool) [0x88a7bd]
source/dub/dub.d:1249 dub.dependency.Dependency[immutable(char)[]] dub.dub.DependencyVersionResolver.resolve(dub.package_.Package, dub.project.SelectedVersions) [0x896c7e]
source/dub/dub.d:413 void dub.dub.Dub.upgrade(dub.dub.UpgradeOptions, immutable(char)[][]) [0x890d6b]
source/dub/commandline.d:1155 int dub.commandline.UpgradeCommand.execute(dub.dub.Dub, immutable(char)[][], immutable(char)[][]) [0x85937d]
source/dub/commandline.d:239 int dub.commandline.runDubCommandLine(immutable(char)[][]) [0x853647]
source/app.d:14 _Dmain [0x84fc27]