test: add tests for scopes field in TokenRequest (#640)

* test: add failing test empty scope list

* fix: ignore scopes param if provided an empty list

* revert: change to TokenRequest, test asserts current behavior

* add charset

* chore: fix lint

Author: chingor13

google-oauth-client/src/test/java/com/google/api/client/auth/oauth2/TokenRequestTest.java

@@ -15,8 +15,14 @@
 package com.google.api.client.auth.oauth2;
 
 import com.google.api.client.http.GenericUrl;
+import com.google.api.client.http.HttpContent;
+import com.google.api.client.http.UrlEncodedContent;
 import com.google.api.client.json.gson.GsonFactory;
 import com.google.api.client.testing.http.MockHttpTransport;
+import com.google.common.collect.ImmutableList;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
 import junit.framework.TestCase;
 
 /**
@@ -45,4 +51,36 @@ static void check(TokenRequest request, String grantType) {
     assertEquals(JSON_FACTORY, request.getJsonFactory());
     assertEquals(AUTHORIZATION_SERVER_URL, request.getTokenServerUrl());
   }
+
+  public void testScopes() throws IOException {
+    TokenRequest request =
+        new TokenRequest(TRANSPORT, JSON_FACTORY, AUTHORIZATION_SERVER_URL, "foo")
+            .setScopes(ImmutableList.of("scope1"));
+    HttpContent content = new UrlEncodedContent(request);
+    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
+    content.writeTo(outputStream);
+    String encoded = new String(outputStream.toByteArray(), StandardCharsets.UTF_8);
+    assertEquals("grant_type=foo&scope=scope1", encoded);
+  }
+
+  public void testEmptyScopes() throws IOException {
+    TokenRequest request =
+        new TokenRequest(TRANSPORT, JSON_FACTORY, AUTHORIZATION_SERVER_URL, "foo")
+            .setScopes(ImmutableList.<String>of());
+    HttpContent content = new UrlEncodedContent(request);
+    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
+    content.writeTo(outputStream);
+    String encoded = new String(outputStream.toByteArray(), StandardCharsets.UTF_8);
+    assertEquals("grant_type=foo&scope", encoded);
+  }
+
+  public void testNullScopes() throws IOException {
+    TokenRequest request =
+        new TokenRequest(TRANSPORT, JSON_FACTORY, AUTHORIZATION_SERVER_URL, "foo").setScopes(null);
+    HttpContent content = new UrlEncodedContent(request);
+    ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
+    content.writeTo(outputStream);
+    String encoded = new String(outputStream.toByteArray(), StandardCharsets.UTF_8);
+    assertEquals("grant_type=foo", encoded);
+  }
 }