Clean up testing with clocks.

service/src/test/java/org/whispersystems/textsecuregcm/util/TestClock.java

@@ -0,0 +1,88 @@
+package org.whispersystems.textsecuregcm.util;
+
+import java.time.Duration;
+import java.time.Instant;
+import java.time.ZoneId;
+import java.util.Optional;
+
+/**
+ * Clock class specialized for testing.
+ *
+ * This clock can be pinned to a particular instant or can provide the "normal" time.
+ *
+ * Unlike normal clocks it can be dynamically pinned and unpinned to help with testing.
+ * It should not be used in production.
+ */
+public class TestClock extends java.time.Clock {
+
+  private Optional<Instant> pinnedInstant;
+  private final ZoneId zoneId;
+
+  private TestClock(Optional<Instant> maybePinned, ZoneId id) {
+    this.pinnedInstant = maybePinned;
+    this.zoneId = id;
+  }
+
+  /**
+   * Instantiate a test clock that returns the "real" time.
+   *
+   * The clock can later be pinned to an instant if desired.
+   *
+   * @return
+   */
+  public static TestClock now() {
+    return new TestClock(Optional.empty(), ZoneId.of("UTC"));
+  }
+
+  /**
+   * Instantiate a test clock pinned to a particular instant.
+   *
+   * The clock can later be pinned to a different instant or unpinned if desired.
+   *
+   * Unlike the fixed constructor no time zone is required (it defaults to UTC).
+   *
+   * @param instant
+   * @return test clock pinned to the given instant.
+   */
+  public static TestClock pinned(Instant instant) {
+    return new TestClock(Optional.of(instant), ZoneId.of("UTC"));
+  }
+
+  /**
+   * Pin this test clock to the given instance.
+   *
+   * This modifies the existing clock in-place.
+   *
+   * @param instant
+   */
+  public void pin(Instant instant) {
+    this.pinnedInstant = Optional.of(instant);
+  }
+
+  /**
+   * Unpin this test clock so it will being returning the "real" time.
+   *
+   * This modifies the existing clock in-place.
+   */
+  public void unpin() {
+    this.pinnedInstant = Optional.empty();
+  }
+
+
+  public TestClock withZone(ZoneId id) {
+    return new TestClock(pinnedInstant, id);
+  }
+
+  public ZoneId getZone() {
+    return zoneId;
+  }
+
+  public Instant instant() {
+    return pinnedInstant.orElseGet(Instant::now);
+  }
+
+  public long millis() {
+    return instant().toEpochMilli();
+  }
+
+}