Refector metrics truth subject

The concrete implementation of a Metric is not of importance when asserting on the values it contains. Therefore this CL removes Metric<T> as a type parameter of AbstractMetricSubject. As a result the two implementations of the abstract subject can be used on any Metric<Long> and Metric<Distribution>, respectively.

Also migrate to Subject.Factory from deprecated SubjectFactory.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=171012012

java/google/registry/monitoring/metrics/contrib/DistributionMetricSubject.java

@@ -0,0 +1,104 @@
+// 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.monitoring.metrics.contrib;
+
+import static com.google.common.truth.Truth.assertAbout;
+
+import com.google.common.collect.BoundType;
+import com.google.common.collect.Range;
+import com.google.common.truth.FailureMetadata;
+import com.google.common.truth.Subject;
+import google.registry.monitoring.metrics.Distribution;
+import google.registry.monitoring.metrics.Metric;
+import google.registry.monitoring.metrics.MetricPoint;
+import java.util.Map;
+import javax.annotation.Nullable;
+
+/**
+ * Truth subject for the {@link Metric<Distribution>} class.
+ *
+ * <p>For use with the Google <a href="https://google.github.io/truth/">Truth</a> framework. Usage:
+ *
+ * <pre>  assertThat(myDistributionMetric)
+ *       .hasAnyValueForLabels("label1", "label2", "label3")
+ *       .and()
+ *       .hasNoOtherValues();
+ *   assertThat(myDistributionMetric)
+ *       .doesNotHaveAnyValueForLabels("label1", "label2");
+ * </pre>
+ *
+ * <p>The assertions treat an empty distribution as no value at all. This is not how the data is
+ * actually stored; event metrics do in fact have an empty distribution after they are reset. But
+ * it's difficult to write assertions about expected metric data when any number of empty
+ * distributions can also be present, so they are screened out for convenience.
+ */
+public final class DistributionMetricSubject
+    extends AbstractMetricSubject<Distribution, DistributionMetricSubject> {
+
+  /** {@link Subject.Factory} for assertions about {@link Metric<Distribution>} objects. */
+  private static final Subject.Factory<DistributionMetricSubject, Metric<Distribution>>
+      SUBJECT_FACTORY =
+          // The Truth extensibility documentation indicates that the target should be nullable.
+          (FailureMetadata failureMetadata, @Nullable Metric<Distribution> target) ->
+              new DistributionMetricSubject(failureMetadata, target);
+
+  /** Static assertThat({@link Metric<Distribution>}) shortcut method. */
+  public static DistributionMetricSubject assertThat(@Nullable Metric<Distribution> metric) {
+    return assertAbout(SUBJECT_FACTORY).that(metric);
+  }
+
+  private DistributionMetricSubject(FailureMetadata metadata, Metric<Distribution> actual) {
+    super(metadata, actual);
+  }
+
+  /**
+   * Returns an indication to {@link AbstractMetricSubject#hasNoOtherValues} on whether a {@link
+   * MetricPoint} has a non-empty distribution.
+   */
+  @Override
+  protected boolean hasDefaultValue(MetricPoint<Distribution> metricPoint) {
+    return metricPoint.value().count() == 0;
+  }
+
+  /** Returns an appropriate string representation of a metric value for use in error messages. */
+  @Override
+  protected String getMessageRepresentation(Distribution distribution) {
+    StringBuilder sb = new StringBuilder("{");
+    boolean first = true;
+    for (Map.Entry<Range<Double>, Long> entry :
+        distribution.intervalCounts().asMapOfRanges().entrySet()) {
+      if (entry.getValue() != 0L) {
+        if (first) {
+          first = false;
+        } else {
+          sb.append(',');
+        }
+        if (entry.getKey().hasLowerBound()) {
+          sb.append((entry.getKey().lowerBoundType() == BoundType.CLOSED) ? '[' : '(');
+          sb.append(entry.getKey().lowerEndpoint());
+        }
+        sb.append("..");
+        if (entry.getKey().hasUpperBound()) {
+          sb.append(entry.getKey().upperEndpoint());
+          sb.append((entry.getKey().upperBoundType() == BoundType.CLOSED) ? ']' : ')');
+        }
+        sb.append('=');
+        sb.append(entry.getValue());
+      }
+    }
+    sb.append('}');
+    return sb.toString();
+  }
+}