diff --git a/java/com/google/gerrit/server/quota/DefaultQuotaBackend.java b/java/com/google/gerrit/server/quota/DefaultQuotaBackend.java
index 8aa86b1..baa7677 100644
--- a/java/com/google/gerrit/server/quota/DefaultQuotaBackend.java
+++ b/java/com/google/gerrit/server/quota/DefaultQuotaBackend.java
@@ -75,7 +75,7 @@
         }
       } catch (RuntimeException e) {
         logger.atSevere().withCause(e).log("exception while enforcing quota");
-        responses.add(QuotaResponse.error(e.getMessage()));
+        responses.add(QuotaResponse.error("failed to request quota tokens"));
       }
     }
 
@@ -97,7 +97,7 @@
         deduct ? "(deduction=yes)" : "(deduction=no)",
         numTokens,
         responses);
-    return new AutoValue_QuotaResponse_Aggregated(ImmutableList.copyOf(responses));
+    return QuotaResponse.Aggregated.create(ImmutableList.copyOf(responses));
   }
 
   static class WithUser extends WithResource implements QuotaBackend.WithUser {
diff --git a/java/com/google/gerrit/server/quota/QuotaResponse.java b/java/com/google/gerrit/server/quota/QuotaResponse.java
index c239aaf..9a8a515 100644
--- a/java/com/google/gerrit/server/quota/QuotaResponse.java
+++ b/java/com/google/gerrit/server/quota/QuotaResponse.java
@@ -20,6 +20,7 @@
 import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Streams;
+import java.util.Collection;
 import java.util.Optional;
 import java.util.stream.Collectors;
 
@@ -77,6 +78,10 @@
 
   @AutoValue
   public abstract static class Aggregated {
+    public static Aggregated create(Collection<QuotaResponse> responses) {
+      return new AutoValue_QuotaResponse_Aggregated(ImmutableList.copyOf(responses));
+    }
+
     protected abstract ImmutableList<QuotaResponse> responses();
 
     public boolean hasError() {
diff --git a/javatests/com/google/gerrit/acceptance/server/quota/BUILD b/javatests/com/google/gerrit/acceptance/server/quota/BUILD
new file mode 100644
index 0000000..1988b22
--- /dev/null
+++ b/javatests/com/google/gerrit/acceptance/server/quota/BUILD
@@ -0,0 +1,7 @@
+load("//javatests/com/google/gerrit/acceptance:tests.bzl", "acceptance_tests")
+
+acceptance_tests(
+    srcs = glob(["*IT.java"]),
+    group = "server_quota",
+    labels = ["server"],
+)
diff --git a/javatests/com/google/gerrit/acceptance/server/quota/DefaultQuotaBackendIT.java b/javatests/com/google/gerrit/acceptance/server/quota/DefaultQuotaBackendIT.java
new file mode 100644
index 0000000..f60d301
--- /dev/null
+++ b/javatests/com/google/gerrit/acceptance/server/quota/DefaultQuotaBackendIT.java
@@ -0,0 +1,158 @@
+// Copyright (C) 2018 The Android Open Source Project
+//
+// 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.gerrit.acceptance.server.quota;
+
+import static com.google.common.truth.Truth.assertThat;
+import static org.easymock.EasyMock.expect;
+import static org.easymock.EasyMock.replay;
+import static org.easymock.EasyMock.resetToStrict;
+
+import com.google.gerrit.acceptance.AbstractDaemonTest;
+import com.google.gerrit.extensions.annotations.Exports;
+import com.google.gerrit.extensions.config.FactoryModule;
+import com.google.gerrit.reviewdb.client.Change;
+import com.google.gerrit.server.IdentifiedUser;
+import com.google.gerrit.server.quota.QuotaBackend;
+import com.google.gerrit.server.quota.QuotaEnforcer;
+import com.google.gerrit.server.quota.QuotaException;
+import com.google.gerrit.server.quota.QuotaRequestContext;
+import com.google.gerrit.server.quota.QuotaResponse;
+import com.google.inject.Inject;
+import com.google.inject.Module;
+import java.util.Collections;
+import org.easymock.EasyMock;
+import org.junit.Before;
+import org.junit.Test;
+
+public class DefaultQuotaBackendIT extends AbstractDaemonTest {
+
+  private static final QuotaEnforcer quotaEnforcer = EasyMock.createStrictMock(QuotaEnforcer.class);
+
+  private IdentifiedUser identifiedAdmin;
+  @Inject private QuotaBackend quotaBackend;
+
+  @Override
+  public Module createModule() {
+    return new FactoryModule() {
+      @Override
+      public void configure() {
+        bind(QuotaEnforcer.class)
+            .annotatedWith(Exports.named("TestQuotaEnforcer"))
+            .toProvider(() -> quotaEnforcer);
+      }
+    };
+  }
+
+  @Before
+  public void setUp() {
+    identifiedAdmin = identifiedUserFactory.create(admin.id);
+    resetToStrict(quotaEnforcer);
+  }
+
+  @Test
+  public void requestTokenForUser() {
+    QuotaRequestContext ctx = QuotaRequestContext.builder().user(identifiedAdmin).build();
+    expect(quotaEnforcer.requestTokens("testGroup", ctx, 1)).andReturn(QuotaResponse.ok());
+    replay(quotaEnforcer);
+    assertThat(quotaBackend.user(identifiedAdmin).requestToken("testGroup"))
+        .isEqualTo(singletonAggregation(QuotaResponse.ok()));
+  }
+
+  @Test
+  public void requestTokenForUserAndAccount() {
+    QuotaRequestContext ctx =
+        QuotaRequestContext.builder().user(identifiedAdmin).account(user.id).build();
+    expect(quotaEnforcer.requestTokens("testGroup", ctx, 1)).andReturn(QuotaResponse.ok());
+    replay(quotaEnforcer);
+    assertThat(quotaBackend.user(identifiedAdmin).account(user.id).requestToken("testGroup"))
+        .isEqualTo(singletonAggregation(QuotaResponse.ok()));
+  }
+
+  @Test
+  public void requestTokenForUserAndProject() {
+    QuotaRequestContext ctx =
+        QuotaRequestContext.builder().user(identifiedAdmin).project(project).build();
+    expect(quotaEnforcer.requestTokens("testGroup", ctx, 1)).andReturn(QuotaResponse.ok());
+    replay(quotaEnforcer);
+    assertThat(quotaBackend.user(identifiedAdmin).project(project).requestToken("testGroup"))
+        .isEqualTo(singletonAggregation(QuotaResponse.ok()));
+  }
+
+  @Test
+  public void requestTokenForUserAndChange() throws Exception {
+    Change.Id changeId = createChange().getChange().getId();
+    QuotaRequestContext ctx =
+        QuotaRequestContext.builder()
+            .user(identifiedAdmin)
+            .change(changeId)
+            .project(project)
+            .build();
+    expect(quotaEnforcer.requestTokens("testGroup", ctx, 1)).andReturn(QuotaResponse.ok());
+    replay(quotaEnforcer);
+    assertThat(
+            quotaBackend.user(identifiedAdmin).change(changeId, project).requestToken("testGroup"))
+        .isEqualTo(singletonAggregation(QuotaResponse.ok()));
+  }
+
+  @Test
+  public void requestTokens() {
+    QuotaRequestContext ctx = QuotaRequestContext.builder().user(identifiedAdmin).build();
+    expect(quotaEnforcer.requestTokens("testGroup", ctx, 123)).andReturn(QuotaResponse.ok());
+    replay(quotaEnforcer);
+    assertThat(quotaBackend.user(identifiedAdmin).requestTokens("testGroup", 123))
+        .isEqualTo(singletonAggregation(QuotaResponse.ok()));
+  }
+
+  @Test
+  public void dryRun() {
+    QuotaRequestContext ctx = QuotaRequestContext.builder().user(identifiedAdmin).build();
+    expect(quotaEnforcer.dryRun("testGroup", ctx, 123)).andReturn(QuotaResponse.ok());
+    replay(quotaEnforcer);
+    assertThat(quotaBackend.user(identifiedAdmin).dryRun("testGroup", 123))
+        .isEqualTo(singletonAggregation(QuotaResponse.ok()));
+  }
+
+  @Test
+  public void requestTokenError() throws Exception {
+    QuotaRequestContext ctx = QuotaRequestContext.builder().user(identifiedAdmin).build();
+    expect(quotaEnforcer.requestTokens("testGroup", ctx, 1))
+        .andReturn(QuotaResponse.error("failed"));
+    replay(quotaEnforcer);
+
+    QuotaResponse.Aggregated result = quotaBackend.user(identifiedAdmin).requestToken("testGroup");
+    assertThat(result).isEqualTo(singletonAggregation(QuotaResponse.error("failed")));
+    exception.expect(QuotaException.class);
+    exception.expectMessage("failed");
+    result.throwOnError();
+  }
+
+  @Test
+  public void requestTokenPluginThrowsResultsInError() throws Exception {
+    QuotaRequestContext ctx = QuotaRequestContext.builder().user(identifiedAdmin).build();
+    expect(quotaEnforcer.requestTokens("testGroup", ctx, 1)).andThrow(new NullPointerException());
+    replay(quotaEnforcer);
+
+    QuotaResponse.Aggregated result = quotaBackend.user(identifiedAdmin).requestToken("testGroup");
+    assertThat(result)
+        .isEqualTo(singletonAggregation(QuotaResponse.error("failed to request quota tokens")));
+    exception.expect(QuotaException.class);
+    exception.expectMessage("failed to request quota tokens");
+    result.throwOnError();
+  }
+
+  private static QuotaResponse.Aggregated singletonAggregation(QuotaResponse response) {
+    return QuotaResponse.Aggregated.create(Collections.singleton(response));
+  }
+}
diff --git a/javatests/com/google/gerrit/acceptance/server/quota/MultipleQuotaPluginsIT.java b/javatests/com/google/gerrit/acceptance/server/quota/MultipleQuotaPluginsIT.java
new file mode 100644
index 0000000..ba69d7c
--- /dev/null
+++ b/javatests/com/google/gerrit/acceptance/server/quota/MultipleQuotaPluginsIT.java
@@ -0,0 +1,121 @@
+// Copyright (C) 2018 The Android Open Source Project
+//
+// 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.gerrit.acceptance.server.quota;
+
+import static com.google.common.truth.Truth.assertThat;
+import static org.easymock.EasyMock.expect;
+import static org.easymock.EasyMock.expectLastCall;
+import static org.easymock.EasyMock.replay;
+import static org.easymock.EasyMock.resetToStrict;
+
+import com.google.common.collect.ImmutableList;
+import com.google.gerrit.acceptance.AbstractDaemonTest;
+import com.google.gerrit.extensions.annotations.Exports;
+import com.google.gerrit.extensions.config.FactoryModule;
+import com.google.gerrit.server.IdentifiedUser;
+import com.google.gerrit.server.quota.QuotaBackend;
+import com.google.gerrit.server.quota.QuotaEnforcer;
+import com.google.gerrit.server.quota.QuotaRequestContext;
+import com.google.gerrit.server.quota.QuotaResponse;
+import com.google.inject.Inject;
+import com.google.inject.Module;
+import org.easymock.EasyMock;
+import org.junit.Before;
+import org.junit.Test;
+
+public class MultipleQuotaPluginsIT extends AbstractDaemonTest {
+  private static final QuotaEnforcer quotaEnforcerA =
+      EasyMock.createStrictMock(QuotaEnforcer.class);
+  private static final QuotaEnforcer quotaEnforcerB =
+      EasyMock.createStrictMock(QuotaEnforcer.class);
+
+  private IdentifiedUser identifiedAdmin;
+  @Inject private QuotaBackend quotaBackend;
+
+  @Override
+  public Module createModule() {
+    return new FactoryModule() {
+      @Override
+      public void configure() {
+        bind(QuotaEnforcer.class)
+            .annotatedWith(Exports.named("TestQuotaEnforcerA"))
+            .toProvider(() -> quotaEnforcerA);
+
+        bind(QuotaEnforcer.class)
+            .annotatedWith(Exports.named("TestQuotaEnforcerB"))
+            .toProvider(() -> quotaEnforcerB);
+      }
+    };
+  }
+
+  @Before
+  public void setUp() {
+    identifiedAdmin = identifiedUserFactory.create(admin.id);
+    resetToStrict(quotaEnforcerA);
+    resetToStrict(quotaEnforcerB);
+  }
+
+  @Test
+  public void refillsOnError() {
+    QuotaRequestContext ctx = QuotaRequestContext.builder().user(identifiedAdmin).build();
+    expect(quotaEnforcerA.requestTokens("testGroup", ctx, 1)).andReturn(QuotaResponse.ok());
+    expect(quotaEnforcerB.requestTokens("testGroup", ctx, 1))
+        .andReturn(QuotaResponse.error("fail"));
+    quotaEnforcerA.refill("testGroup", ctx, 1);
+    expectLastCall();
+
+    replay(quotaEnforcerA);
+    replay(quotaEnforcerB);
+
+    assertThat(quotaBackend.user(identifiedAdmin).requestToken("testGroup"))
+        .isEqualTo(
+            QuotaResponse.Aggregated.create(
+                ImmutableList.of(QuotaResponse.ok(), QuotaResponse.error("fail"))));
+  }
+
+  @Test
+  public void refillsOnException() {
+    QuotaRequestContext ctx = QuotaRequestContext.builder().user(identifiedAdmin).build();
+    expect(quotaEnforcerA.requestTokens("testGroup", ctx, 1)).andReturn(QuotaResponse.ok());
+    expect(quotaEnforcerB.requestTokens("testGroup", ctx, 1)).andThrow(new NullPointerException());
+    quotaEnforcerA.refill("testGroup", ctx, 1);
+    expectLastCall();
+
+    replay(quotaEnforcerA);
+    replay(quotaEnforcerB);
+
+    assertThat(quotaBackend.user(identifiedAdmin).requestToken("testGroup"))
+        .isEqualTo(
+            QuotaResponse.Aggregated.create(
+                ImmutableList.of(
+                    QuotaResponse.ok(), QuotaResponse.error("failed to request quota tokens"))));
+  }
+
+  @Test
+  public void doesNotRefillNoOp() {
+    QuotaRequestContext ctx = QuotaRequestContext.builder().user(identifiedAdmin).build();
+    expect(quotaEnforcerA.requestTokens("testGroup", ctx, 1))
+        .andReturn(QuotaResponse.error("fail"));
+    expect(quotaEnforcerB.requestTokens("testGroup", ctx, 1)).andReturn(QuotaResponse.noOp());
+
+    replay(quotaEnforcerA);
+    replay(quotaEnforcerB);
+
+    assertThat(quotaBackend.user(identifiedAdmin).requestToken("testGroup"))
+        .isEqualTo(
+            QuotaResponse.Aggregated.create(
+                ImmutableList.of(QuotaResponse.error("fail"), QuotaResponse.noOp())));
+  }
+}