For #3869 - Fixes unit tests

app/src/test/java/org/mozilla/fenix/components/TestCore.kt

@@ -9,6 +9,7 @@ import io.mockk.mockk
 import mozilla.components.browser.engine.gecko.GeckoEngine
 import mozilla.components.browser.session.SessionManager
 import mozilla.components.browser.state.store.BrowserStore
+import mozilla.components.concept.fetch.Client
 import mozilla.components.feature.pwa.WebAppShortcutManager
 import mozilla.components.lib.dataprotect.SecureAbove22Preferences
 
@@ -17,6 +18,7 @@ class TestCore(context: Context) : Core(context) {
     override val engine = mockk<GeckoEngine>(relaxed = true)
     override val sessionManager = SessionManager(engine)
     override val store = mockk<BrowserStore>()
+    override val client = mockk<Client>()
     override val webAppShortcutManager = mockk<WebAppShortcutManager>()
     override fun getSecureAbove22Preferences() = mockk<SecureAbove22Preferences>(relaxed = true)
 }