I have an `object` as a wrapper for Android shared preferenc

Question

I have an `object` as a wrapper for Android shared preferences The preferences are lazily initialized and `object` properties are delegated to the preferences like this ```object Persistence private val prefs by lazy PreferencesUtil ContextProvider context val timestamp by prefs readOnlyLongPref R string timestamp 0L ``` I want to mock the object for tests of another class where `Persistence` is a dependency The problem is even if I don t reference this object instance in the class under test but just as a type i e `class CartRepository private val persistence Persistence ` still the test fails with an exception telling that `ContextProvider context` has not been initialized

Lukasz Kalnik · Answer

The stack trace actually says that the first delegated property is being resolved it is in line 32 in code and that s why the `lazy` actually it s a custom `MutableLazy` in this case but the principle is the same is executed to get the `prefs` value for the delegate ```Caused by kotlin UninitializedPropertyAccessException lateinit property context has not been initialized at package redacted util util ContextProvider$Companion getContext ContextProvider kt 8 at package redacted core support Persistence$prefs$2 invoke Persistence kt 26 at package redacted core support Persistence$prefs$2 invoke Persistence kt 26 at package redacted util util MutableLazy getValue MutableLazy kt 24 at package redacted core support Persistence getPrefs Persistence kt 26 at package redacted core support Persistence lt clinit gt Persistence kt 32 ```

Lukasz Kalnik · Answer

I find it interesting that even though I only access the `Persistence` type not the instance itself still the instance is apparently being created automatically at the same time in `clinit`

Lukasz Kalnik · Answer

And the delegates are being resolved immediately

Lukasz Kalnik · Answer

I guess for tests I will just have to hide the `Persistence` behind an interface

lazynoda · Answer

The problem is how Kotlin compiles this into bytecode An `object` is a singleton created when the app starts so the `Persistence` instance is created Then checking the Kotlin bytecode apparently the delegates are also instantiated so this is calling `prefs readOnly ` so `prefs` is created Maybe consider switching to ```val timestamp Long get = prefs readLongPref ```

lazynoda · Answer

btw Android studio and I guess IntelliJ too has a tool to see the Kotlin bytecode Tools Kotlin Show bytecode and then switch back to Java via Decompile button That s how I knew it You find pretty good info how things are created and managed under the hood

Lukasz Kalnik · Answer

Yes actually even hiding `Persistence` behind an interface didn t get rid of this error

Lukasz Kalnik · Answer

The approach with `get ` could probably work but defeats the convenience of having delegates

lazynoda · Answer

But it works in both tests and production smile

Lukasz Kalnik · Answer

Yes slightly smiling face

lazynoda · Answer

I m not a fan of changing production code because of the tests but `get =` doesn t add extra steps overhead whatever In fact is a more direct access to the data isn t it

Lukasz Kalnik · Answer

Yes but you need `get set ` instead of just using `by`

Lukasz Kalnik · Answer

And you have to do it for every property

Lukasz Kalnik · Answer

Sorry my original example wasn t complete we also have `var` properties

Lukasz Kalnik · Answer

I think maybe we should switch to another dependency injection approach

lazynoda · Answer

What about not using an `object` but a `class` and then injecting the dependency If you need a singleton mandatory let the DI framework to take care of it

Lukasz Kalnik · Answer

Yes that could be a solution here

Lukasz Kalnik · Answer

This is a library so we were avoiding adding a DI framework so far to not bloat the size

lazynoda · Answer

Untitled cpp

Lukasz Kalnik · Answer

Thanks that s also a good approach

Lukasz Kalnik · Answer

Thank you for your helpful suggestions