Sc methods test (#274)

* Add current service client list and test ensuring list is accurate

* google-java-format

* Add generator class and refactor test

* Address comments

Author: devchas

google-ads/src/main/java/com/google/ads/googleads/lib/MethodsListGenerator.java

@@ -0,0 +1,48 @@
+// Copyright 2020 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.ads.googleads.lib;
+import com.google.common.base.Charsets;
+import com.google.common.io.CharSink;
+import com.google.common.io.Files;
+import java.io.File;
+import java.io.IOException;
+import java.lang.reflect.Method;
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * Generates a list of methods present in the GoogleAdsAllVersions class of the latest available
+ * version of the Google Ads API and saves the output to a txt file in the test resources directory.
+ */
+public class MethodsListGenerator {
+  public static void main(String args[])
+      throws ClassNotFoundException, IOException, NoSuchMethodException {
+    Method latestVersionMethod = GoogleAdsAllVersions.class.getMethod("getLatestVersion");
+    Class cls = Class.forName(latestVersionMethod.getReturnType().getName());
+    List<Method> methods = Arrays.asList(cls.getDeclaredMethods());
+
+    StringBuilder output = new StringBuilder();
+    for (Method method : methods) {
+      output.append(method + "\n");
+    }
+
+    System.out.println("Writing the following methods to file:");
+    System.out.printf(output.toString());
+
+    File file = new File("./google-ads/src/test/resources/testdata/avail_service_clients.txt");
+    CharSink sink = Files.asCharSink(file, Charsets.UTF_8);
+    sink.write(output);
+  }
+}

google-ads/src/test/java/com/google/ads/googleads/lib/MethodsPresenceTest.java

@@ -0,0 +1,66 @@
+// Copyright 2020 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.ads.googleads.lib;
+
+import com.google.common.base.Charsets;
+import com.google.common.io.Resources;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+import java.io.IOException;
+import java.lang.reflect.Method;
+import java.net.URL;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+import static org.junit.Assert.assertEquals;
+
+@RunWith(JUnit4.class)
+public class MethodsPresenceTest {
+  /**
+   * Verifies that the list of all service client methods in a given GoogleAdsVersion class matches
+   * that provided in the testdata/avail_service_clients.txt file.
+   *
+   * <p>The avail_service_clients.txt file should be the standard against which all releases are
+   * compared. In the event the list of services changes in the API, this test will fail. Then,
+   * avail_service_clients.txt should be updated so that this test passes.
+   */
+  @Test
+  public void methodsListMatches()
+      throws ClassNotFoundException, NoSuchMethodException, IOException {
+    // Gets the fully qualified return type of the GoogleAdsAllVersions getLatestVersion method,
+    // which is the class from which the methods will be retrieved.
+    Method latestVersionMethod = GoogleAdsAllVersions.class.getMethod("getLatestVersion");
+    Class cls = Class.forName(latestVersionMethod.getReturnType().getName());
+
+    // Retrieves a list of the methods in the GoogleAdsVersion class using reflection and adds
+    // each to a set.
+    List<Method> methods = Arrays.asList(cls.getDeclaredMethods());
+    Set<String> serviceListReflection = new HashSet<>();
+    for (Method method : methods) {
+      serviceListReflection.add(method.toString());
+    }
+
+    // Retrieves the list of service client methods in the provided avail_service_clients.txt file.
+    URL resource = Resources.getResource("testdata/avail_service_clients.txt");
+    Set<String> serviceListResource =
+        new HashSet<>(Resources.asCharSource(resource, Charsets.UTF_8).readLines());
+    serviceListResource.remove("");
+
+    assertEquals(serviceListResource, serviceListReflection);
+  }
+}