Modify SmokeTest so it passes for manager accounts (#531)

Fixes two issues:

1. Clears the login customer ID in case ads.properties happens to
   set it. This avoids errors if the credentials grant access to
   accounts in different hierarchies.
2. Queries customers instead of campaigns so queries return results
   even if the credentials only have access to manager accounts.

Author: jradcliff

google-ads/src/test/functional/java/com/google/ads/googleads/lib/SmokeTest.java

@@ -41,24 +41,34 @@
  *
  * <p>Only depends on a basic configuration file with devtoken, OAuth etc.
  *
- * <p>Retrieves all accessible customers and iterates through all their campaigns.
+ * <p>Retrieves all accessible customers and issues a search request for each customer.
  */
 @RunWith(JUnit4.class)
 public class SmokeTest {
 
   @Rule public Timeout timeout = new Timeout(20_000, TimeUnit.MILLISECONDS);
 
   @Test
-  public void ensureCanReadAllAvailableCustomersCampaigns() throws IOException {
-    GoogleAdsClient client = GoogleAdsClient.newBuilder().fromPropertiesFile().build();
+  public void ensureCanReadAllAvailableCustomers() throws IOException {
+    GoogleAdsClient client =
+        GoogleAdsClient.newBuilder()
+            .fromPropertiesFile()
+            // Sets the login-customer-id to null. If this is set in the properties file, then
+            // attempts to issue requests against accessible accounts in a different manager account
+            // hierarchy will fail. With login-customer-id not set, the Google Ads API will set it
+            // to the customer ID in each search request, which will result in a successful request
+            // because this test only queries customers who are directly accessible with the
+            // provided credentials.
+            .setLoginCustomerId(null)
+            .build();
     List<String> accessibleCustomerIds = getAvailableCustomerIds(client);
     if (accessibleCustomerIds.isEmpty()) {
       fail(
           "No accessible customers returned by CustomerService.ListAccessibleCustomers(). Please"
               + " provide a refresh token which has access to customers in order to run functional"
               + " tests");
     }
-    fetchAllCampaigns(client, accessibleCustomerIds);
+    fetchAllCustomers(client, accessibleCustomerIds);
   }
 
   private static List<String> getAvailableCustomerIds(GoogleAdsClient client) {
@@ -76,22 +86,22 @@ private static List<String> getAvailableCustomerIds(GoogleAdsClient client) {
     }
   }
 
-  private static void fetchAllCampaigns(
+  /** Fetches the {@code Customer} object for each accessible customer. */
+  private static void fetchAllCustomers(
       GoogleAdsClient client, List<String> accessibleCustomerIds) {
-    int numCampaigns = 0;
+    int numCustomers = 0;
     try (GoogleAdsServiceClient googleAdsServiceClient =
         client.getLatestVersion().createGoogleAdsServiceClient()) {
       for (String customerId : accessibleCustomerIds) {
         SearchPagedResponse response =
             googleAdsServiceClient.search(
                 customerId,
-                "SELECT campaign.id, campaign.status, campaign.start_date "
-                    + "FROM campaign "
-                    + "WHERE campaign.status != 'REMOVED'");
-        numCampaigns += StreamSupport.stream(response.iterateAll().spliterator(), false).count();
+                "SELECT customer.id, customer.manager, customer.currency_code,"
+                    + " customer.descriptive_name FROM customer");
+        numCustomers += StreamSupport.stream(response.iterateAll().spliterator(), false).count();
       }
     }
-    System.out.println("Retrieved " + numCampaigns + " campaigns");
-    assertTrue("Expected to read at least one campaign for smoke test.", numCampaigns > 0);
+    System.out.println("Retrieved " + numCustomers + " customers");
+    assertTrue("Expected to read at least one customer for smoke test.", numCustomers > 0);
   }
 }