README.md

This test is to verify if preferencesDataStore will be updated on-the-fly. After running this, !UpdatedPref 1! and !UpdatedPref 2! was printed.

(On confirming this question on SO)

PreferencesDataStoreTest.kt

package com.github.kentvu.test

import android.util.Log
import androidx.datastore.preferences.core.edit
import androidx.datastore.preferences.core.stringPreferencesKey
import androidx.test.ext.junit.runners.AndroidJUnit4
import kotlinx.coroutines.launch
import kotlinx.coroutines.runBlocking
import kotlinx.coroutines.withTimeout
import org.junit.Test
import org.junit.runner.RunWith

val Context.dataStore: DataStore<Preferences> by preferencesDataStore(name = "settings")

@RunWith(AndroidJUnit4::class)
class PreferencesDataStoreTest {
  @Test
  fun isDataStoreUpdatedOnTheFly(): Unit = runBlocking {
    val appContext = InstrumentationRegistry.getInstrumentation().targetContext
    val key = stringPreferencesKey("test")
    launch {
      withTimeout(10.seconds) {
        appContext.dataStore.data.collect { prefs ->
          Log.i("DefaultSettingsTest", "Prefs updated: " + prefs[key])
        }
      }
    }
    appContext.dataStore.edit { prefs -> prefs[key] = "!UpdatedPref 1!" }
    appContext.dataStore.edit { prefs -> prefs[key] = "!UpdatedPref 2!" }
  }
}