Metrics/TimeSeries: Add createWithOnePoint method to accept only one … (#1486)

* Metrics/TimeSeries: Add createWithOnePoint method to accept only one point

* Fix reviews

* Minor Fix

2 files changed, 68 insertions, 3 deletions

diff --git a/api/src/main/java/io/opencensus/metrics/export/TimeSeries.java b/api/src/main/java/io/opencensus/metrics/export/TimeSeries.java
index 959f55ba..bfaeae98 100644
--- a/api/src/main/java/io/opencensus/metrics/export/TimeSeries.java
+++ b/api/src/main/java/io/opencensus/metrics/export/TimeSeries.java
@@ -52,14 +52,45 @@ public abstract class TimeSeries {
    */
   public static TimeSeries create(
       List<LabelValue> labelValues, List<Point> points, @Nullable Timestamp startTimestamp) {
+    Utils.checkNotNull(points, "points");
+    Utils.checkListElementNotNull(points, "point");
+    return createInternal(
+        labelValues, Collections.unmodifiableList(new ArrayList<Point>(points)), startTimestamp);
+  }
+
+  /**
+   * Creates a {@link TimeSeries}.
+   *
+   * @param labelValues the {@code LabelValue}s that uniquely identify this {@code TimeSeries}.
+   * @param point the single data {@code Point} of this {@code TimeSeries}.
+   * @param startTimestamp the start {@code Timestamp} of this {@code TimeSeries}. Must be non-null
+   *     for cumulative {@code Point}s.
+   * @return a {@code TimeSeries}.
+   * @since 0.17
+   */
+  public static TimeSeries createWithOnePoint(
+      List<LabelValue> labelValues, Point point, @Nullable Timestamp startTimestamp) {
+    Utils.checkNotNull(point, "point");
+    return createInternal(labelValues, Collections.singletonList(point), startTimestamp);
+  }
+
+  /**
+   * Creates a {@link TimeSeries}.
+   *
+   * @param labelValues the {@code LabelValue}s that uniquely identify this {@code TimeSeries}.
+   * @param points the data {@code Point}s of this {@code TimeSeries}.
+   * @param startTimestamp the start {@code Timestamp} of this {@code TimeSeries}. Must be non-null
+   *     for cumulative {@code Point}s.
+   * @return a {@code TimeSeries}.
+   */
+  private static TimeSeries createInternal(
+      List<LabelValue> labelValues, List<Point> points, @Nullable Timestamp startTimestamp) {
     // Fail fast on null lists to prevent NullPointerException when copying the lists.
     Utils.checkNotNull(labelValues, "labelValues");
-    Utils.checkNotNull(points, "points");
     Utils.checkListElementNotNull(labelValues, "labelValue");
-    Utils.checkListElementNotNull(points, "point");
     return new AutoValue_TimeSeries(
         Collections.unmodifiableList(new ArrayList<LabelValue>(labelValues)),
-        Collections.unmodifiableList(new ArrayList<Point>(points)),
+        points,
         startTimestamp);
   }
 
diff --git a/api/src/test/java/io/opencensus/metrics/export/TimeSeriesTest.java b/api/src/test/java/io/opencensus/metrics/export/TimeSeriesTest.java
index 31812549..92a2c8cf 100644
--- a/api/src/test/java/io/opencensus/metrics/export/TimeSeriesTest.java
+++ b/api/src/test/java/io/opencensus/metrics/export/TimeSeriesTest.java
@@ -90,6 +90,40 @@ public class TimeSeriesTest {
   }
 
   @Test
+  public void testGet_WithOnePointTimeSeries() {
+    TimeSeries cumulativeTimeSeries =
+        TimeSeries.createWithOnePoint(
+            Arrays.asList(LABEL_VALUE_1, LABEL_VALUE_2), POINT_1, TIMESTAMP_1);
+    assertThat(cumulativeTimeSeries.getStartTimestamp()).isEqualTo(TIMESTAMP_1);
+    assertThat(cumulativeTimeSeries.getLabelValues())
+        .containsExactly(LABEL_VALUE_1, LABEL_VALUE_2)
+        .inOrder();
+    assertThat(cumulativeTimeSeries.getPoints()).containsExactly(POINT_1).inOrder();
+  }
+
+  @Test
+  public void createWithOnePoint_WithNullLabelValueList() {
+    thrown.expect(NullPointerException.class);
+    thrown.expectMessage(CoreMatchers.equalTo("labelValues"));
+    TimeSeries.createWithOnePoint(null, POINT_1, TIMESTAMP_1);
+  }
+
+  @Test
+  public void createWithOnePoint_WithNullLabelValue() {
+    List<LabelValue> labelValues = Arrays.asList(LABEL_VALUE_1, null);
+    thrown.expect(NullPointerException.class);
+    thrown.expectMessage(CoreMatchers.equalTo("labelValue"));
+    TimeSeries.createWithOnePoint(labelValues, POINT_1, TIMESTAMP_1);
+  }
+
+  @Test
+  public void createWithOnePoint_WithNullPointList() {
+    thrown.expect(NullPointerException.class);
+    thrown.expectMessage(CoreMatchers.equalTo("point"));
+    TimeSeries.createWithOnePoint(Collections.<LabelValue>emptyList(), null, TIMESTAMP_1);
+  }
+
+  @Test
   public void testEquals() {
     new EqualsTester()
         .addEqualityGroup(