Slight cleanup in GoogleSignInPlugin

1) Use switch instead of if/else and show all possible states
2) Handle the case of synchronous failure in signInSilently()
   by checking isComplete() instead of isSuccessful()

packages/google_sign_in/google_sign_in_android/android/src/main/java/io/flutter/plugins/googlesignin/GoogleSignInPlugin.java

@@ -404,9 +404,9 @@ public void init(
     public void signInSilently(Result result) {
       checkAndSetPendingOperation(METHOD_SIGN_IN_SILENTLY, result);
       Task<GoogleSignInAccount> task = signInClient.silentSignIn();
-      if (task.isSuccessful()) {
+      if (task.isComplete()) {
         // There's immediate result available.
-        onSignInAccount(task.getResult());
+        onSignInResult(task);
       } else {
         task.addOnCompleteListener(
             new OnCompleteListener<GoogleSignInAccount>() {
@@ -516,7 +516,7 @@ private void onSignInResult(Task<GoogleSignInAccount> completedTask) {
         GoogleSignInAccount account = completedTask.getResult(ApiException.class);
         onSignInAccount(account);
       } catch (ApiException e) {
-        // Forward all errors and let Dart side decide how to handle.
+        // Forward all errors and let Dart decide how to handle.
         String errorCode = errorCodeForStatus(e.getStatusCode());
         finishWithError(errorCode, e.toString());
       } catch (RuntimeExecutionException e) {
@@ -538,14 +538,20 @@ private void onSignInAccount(GoogleSignInAccount account) {
     }
 
     private String errorCodeForStatus(int statusCode) {
-      if (statusCode == GoogleSignInStatusCodes.SIGN_IN_CANCELLED) {
-        return ERROR_REASON_SIGN_IN_CANCELED;
-      } else if (statusCode == CommonStatusCodes.SIGN_IN_REQUIRED) {
-        return ERROR_REASON_SIGN_IN_REQUIRED;
-      } else if (statusCode == CommonStatusCodes.NETWORK_ERROR) {
-        return ERROR_REASON_NETWORK_ERROR;
-      } else {
-        return ERROR_REASON_SIGN_IN_FAILED;
+      switch (statusCode) {
+        case GoogleSignInStatusCodes.SIGN_IN_CANCELLED:
+            return ERROR_REASON_SIGN_IN_CANCELED;
+        case CommonStatusCodes.SIGN_IN_REQUIRED:
+            return ERROR_REASON_SIGN_IN_REQUIRED;
+        case CommonStatusCodes.NETWORK_ERROR:
+            return ERROR_REASON_NETWORK_ERROR;
+        case GoogleSignInStatusCodes.SIGN_IN_CURRENTLY_IN_PROGRESS:
+        case GoogleSignInStatusCodes.SIGN_IN_FAILED:
+        case CommonStatusCodes.INVALID_ACCOUNT:
+        case CommonStatusCodes.INTERNAL_ERROR:
+            return ERROR_REASON_SIGN_IN_FAILED;
+        default:
+            return ERROR_REASON_SIGN_IN_FAILED;
       }
     }
 

packages/google_sign_in/google_sign_in_android/android/src/test/java/io/flutter/plugins/googlesignin/GoogleSignInTest.java

@@ -17,7 +17,10 @@
 import com.google.android.gms.auth.api.signin.GoogleSignInAccount;
 import com.google.android.gms.auth.api.signin.GoogleSignInClient;
 import com.google.android.gms.auth.api.signin.GoogleSignInOptions;
+import com.google.android.gms.common.api.ApiException;
 import com.google.android.gms.common.api.Scope;
+import com.google.android.gms.common.api.Status;
+import com.google.android.gms.tasks.Task;
 import io.flutter.plugin.common.BinaryMessenger;
 import io.flutter.plugin.common.MethodCall;
 import io.flutter.plugin.common.MethodChannel;
@@ -43,6 +46,7 @@ public class GoogleSignInTest {
   @Mock GoogleSignInWrapper mockGoogleSignIn;
   @Mock GoogleSignInAccount account;
   @Mock GoogleSignInClient mockClient;
+  @Mock Task<GoogleSignInAccount> mockSignInTask;
   private GoogleSignInPlugin plugin;
 
   @Before
@@ -204,6 +208,22 @@ public void signInThrowsWithoutActivity() {
     plugin.onMethodCall(new MethodCall("signIn", null), null);
   }
 
+  @Test
+  public void signInSilentlyThatImmediatelyCompletesWithoutResultFinishesWithError() {
+    final String clientId = "fakeClientId";
+    MethodCall methodCall = buildInitMethodCall(clientId, null);
+    initAndAssertServerClientId(methodCall, clientId);
+
+    ApiException exception = new ApiException(new Status(CommonStatusCodes.SIGN_IN_REQUIRED, "Error text"));
+    when(mockClient.silentSignIn()).thenReturn(mockSignInTask);
+    when(mockSignInTask.isComplete()).thenReturn(true);
+    when(mockSignInTask.getResult(ApiException.class)).thenThrow(exception);
+
+    MethodCall methodCall = new MethodCall("signInSilently", null);
+    plugin.onMethodCall(methodCall, result);
+    verify(result).error("sign_in_required", "Error text", null);
+  }
+
   @Test
   public void init_LoadsServerClientIdFromResources() {
     final String packageName = "fakePackageName";