Enable flow documentation in external build

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=241934689

javatests/google/registry/documentation/FlowExceptionsTest.java

@@ -0,0 +1,76 @@
+// Copyright 2017 The Nomulus Authors. All Rights Reserved.
+//
+// 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 google.registry.documentation;
+
+import static com.google.common.truth.Truth.assertWithMessage;
+
+import com.google.common.collect.Sets;
+import com.google.common.flogger.FluentLogger;
+import google.registry.documentation.FlowDocumentation.ErrorCase;
+import java.io.IOException;
+import java.util.Set;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/**
+ * Test to ensure accurate documentation of flow exceptions.
+ *
+ * <p>This test goes through each flow and ensures that the exceptions listed in custom javadoc
+ * tags on the flow class match the import statements in the test case for that flow.  Thus it
+ * catches the case where someone adds a test case for an exception without updating the javadoc,
+ * and the case where someone adds a javadoc tag to a flow without writing a test for this error
+ * condition.  For example, there should always be a matching pair of lines such as the following:
+ *
+ * <pre>
+ *   java/.../flows/session/LoginFlow.java:
+ *     @error {&#64;link AlreadyLoggedInException}
+ *
+ *   javatests/.../flows/session/LoginFlowTest.java:
+ *     import .....flows.session.LoginFlow.AlreadyLoggedInException;
+ * </pre>
+ *
+ * If the first line is missing, this test fails and suggests adding the javadoc tag or removing
+ * the import.  If the second line is missing, this test fails and suggests adding the import or
+ * removing the javadoc tag.
+ */
+@SuppressWarnings("javadoc")
+@RunWith(JUnit4.class)
+public class FlowExceptionsTest {
+
+  private static final FluentLogger logger = FluentLogger.forEnclosingClass();
+
+  @Test
+  public void testExceptionCorrespondence() throws IOException {
+    DocumentationGenerator docGenerator = new DocumentationGenerator();
+    Set<ErrorCase> possibleErrors = Sets.newHashSet(docGenerator.getAllErrors());
+    Set<String> mismatchingFlows = Sets.newHashSet();
+    for (FlowDocumentation flow : docGenerator.getFlowDocs()) {
+      FlowContext context = new FlowContext(flow, possibleErrors);
+      String mismatches = context.getMismatchedExceptions();
+      if (!mismatches.isEmpty()) {
+        logger.atWarning().log("%-40s FAIL\n\n%s", flow.getName(), mismatches);
+        mismatchingFlows.add(flow.getName());
+      } else {
+        logger.atInfo().log("%-40s OK", flow.getName());
+      }
+    }
+    assertWithMessage(
+            "Mismatched exceptions between flow documentation and tests. See test log for full "
+                + "details. The set of failing flows follows.")
+        .that(mismatchingFlows)
+        .isEmpty();
+  }
+}