Add tests for the login view models

app/src/test/java/com/github/swent/echo/fakes/FakeAuthenticationService.kt

@@ -0,0 +1,43 @@
+package com.github.swent.echo.fakes
+
+import com.github.swent.echo.authentication.AuthenticationResult
+import com.github.swent.echo.authentication.AuthenticationService
+import java.util.concurrent.CompletableFuture
+import kotlinx.coroutines.future.await
+
+/** A fake implementation of the authentication service. */
+class FakeAuthenticationService : AuthenticationService {
+    private lateinit var signedInResult: CompletableFuture<AuthenticationResult>
+
+    /** The user ID to return when [getCurrentUserID] is called. */
+    var userID: String? = null
+
+    /**
+     * Completes the current signing operation with the given result. Make sure to call this method
+     * after calling [signIn], [signUp], or [signOut].
+     *
+     * @param result The result of the signing operation.
+     */
+    fun completeSigningOperation(result: AuthenticationResult) {
+        signedInResult.complete(result)
+    }
+
+    override suspend fun signIn(email: String, password: String): AuthenticationResult {
+        signedInResult = CompletableFuture()
+        return signedInResult.await()
+    }
+
+    override suspend fun signUp(email: String, password: String): AuthenticationResult {
+        signedInResult = CompletableFuture()
+        return signedInResult.await()
+    }
+
+    override suspend fun signOut(): AuthenticationResult {
+        signedInResult = CompletableFuture()
+        return signedInResult.await()
+    }
+
+    override suspend fun getCurrentUserID(): String? {
+        return userID
+    }
+}

app/src/test/java/com/github/swent/echo/viewmodels/authentication/LoginViewModelTest.kt

@@ -0,0 +1,58 @@
+package com.github.swent.echo.viewmodels.authentication
+
+import com.github.swent.echo.authentication.AuthenticationResult
+import com.github.swent.echo.fakes.FakeAuthenticationService
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.test.UnconfinedTestDispatcher
+import kotlinx.coroutines.test.runTest
+import kotlinx.coroutines.test.setMain
+import org.junit.Assert.assertEquals
+import org.junit.Before
+import org.junit.Test
+
+@OptIn(ExperimentalCoroutinesApi::class)
+class LoginViewModelTest {
+    private lateinit var fakeAuthenticationService: FakeAuthenticationService
+    private lateinit var viewModel: LoginViewModel
+
+    companion object {
+        private const val EMAIL = "test@email.com"
+        private const val PASSWORD = "password"
+    }
+
+    @Before
+    fun setUp() {
+        fakeAuthenticationService = FakeAuthenticationService()
+        viewModel = LoginViewModel(fakeAuthenticationService)
+    }
+
+    @Test
+    fun `state should be signed out when created`() {
+        assertEquals(AuthenticationState.SignedOut, viewModel.state.value)
+    }
+
+    @Test
+    fun `login should return success when successful`() = runTest {
+        val testDispatcher = UnconfinedTestDispatcher(testScheduler)
+        Dispatchers.setMain(testDispatcher)
+
+        viewModel.login(EMAIL, PASSWORD)
+        assertEquals(AuthenticationState.SigningIn, viewModel.state.value)
+        fakeAuthenticationService.completeSigningOperation(AuthenticationResult.Success)
+        assertEquals(AuthenticationState.SignedIn, viewModel.state.value)
+    }
+
+    @Test
+    fun `login should return error when failed`() = runTest {
+        val testDispatcher = UnconfinedTestDispatcher(testScheduler)
+        Dispatchers.setMain(testDispatcher)
+
+        viewModel.login(EMAIL, PASSWORD)
+        assertEquals(AuthenticationState.SigningIn, viewModel.state.value)
+        fakeAuthenticationService.completeSigningOperation(
+            AuthenticationResult.Error("Error message")
+        )
+        assertEquals(AuthenticationState.Error("Error message"), viewModel.state.value)
+    }
+}