Add a register view model

This is very similar to the login view model. This is intentional, because later on the register screen will also handle the user profile creation.

app/src/main/java/com/github/swent/echo/viewmodels/authentication/RegisterViewModel.kt

@@ -0,0 +1,39 @@
+package com.github.swent.echo.viewmodels.authentication
+
+import androidx.lifecycle.ViewModel
+import androidx.lifecycle.viewModelScope
+import com.github.swent.echo.authentication.AuthenticationResult
+import com.github.swent.echo.authentication.AuthenticationService
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.asStateFlow
+import kotlinx.coroutines.launch
+
+/**
+ * ViewModel for the register screen.
+ *
+ * @param auth The authentication service to use.
+ */
+class RegisterViewModel(private val auth: AuthenticationService) : ViewModel() {
+
+    private val _state = MutableStateFlow<AuthenticationState>(AuthenticationState.SignedOut)
+
+    /** The current state of the view model. */
+    val state = _state.asStateFlow()
+
+    /**
+     * Sign up with email and password.
+     *
+     * @param email The email of the user.
+     * @param password The password of the user.
+     */
+    fun register(email: String, password: String) {
+        _state.value = AuthenticationState.SigningIn
+        viewModelScope.launch {
+            when (val result = auth.signUp(email, password)) {
+                is AuthenticationResult.Success -> _state.value = AuthenticationState.SignedIn
+                is AuthenticationResult.Error ->
+                    _state.value = AuthenticationState.Error(result.message)
+            }
+        }
+    }
+}

app/src/test/java/com/github/swent/echo/viewmodels/authentication/RegisterViewModelTest.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 RegisterViewModelTest {
+    private lateinit var fakeAuthenticationService: FakeAuthenticationService
+    private lateinit var viewModel: RegisterViewModel
+
+    companion object {
+        private const val EMAIL = "test@email.com"
+        private const val PASSWORD = "password"
+    }
+
+    @Before
+    fun setUp() {
+        fakeAuthenticationService = FakeAuthenticationService()
+        viewModel = RegisterViewModel(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.register(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.register(EMAIL, PASSWORD)
+        assertEquals(AuthenticationState.SigningIn, viewModel.state.value)
+        fakeAuthenticationService.completeSigningOperation(
+            AuthenticationResult.Error("Error message")
+        )
+        assertEquals(AuthenticationState.Error("Error message"), viewModel.state.value)
+    }
+}