fix: use nanos to prevent truncation errors (#204)

SpannerRetryHelperTest.testExceptionWithRetryInfo could sometimes fail on some
environments. I have not been able to reproduce it locally, but one possible
reason for the failure could be truncation when converting from nanoseconds to
milliseconds. Now both the timeout and the verification use nanosecond precision.

This change also removes all uses of hamcres in this test file.

Fixes #200

google-cloud-spanner/src/test/java/com/google/cloud/spanner/SpannerRetryHelperTest.java

@@ -16,9 +16,7 @@
 
 package com.google.cloud.spanner;
 
-import static org.hamcrest.CoreMatchers.equalTo;
-import static org.hamcrest.CoreMatchers.is;
-import static org.hamcrest.MatcherAssert.assertThat;
+import static com.google.common.truth.Truth.assertThat;
 import static org.junit.Assert.fail;
 
 import com.google.common.base.Stopwatch;
@@ -125,7 +123,7 @@ public Integer call() throws Exception {
             return 1 + 1;
           }
         };
-    assertThat(SpannerRetryHelper.runTxWithRetriesOnAborted(callable), is(equalTo(2)));
+    assertThat(SpannerRetryHelper.runTxWithRetriesOnAborted(callable)).isEqualTo(2);
   }
 
   @Test(expected = IllegalStateException.class)
@@ -153,7 +151,7 @@ public Integer call() throws Exception {
             return 1 + 1;
           }
         };
-    assertThat(SpannerRetryHelper.runTxWithRetriesOnAborted(callable), is(equalTo(2)));
+    assertThat(SpannerRetryHelper.runTxWithRetriesOnAborted(callable)).isEqualTo(2);
   }
 
   @Test
@@ -169,7 +167,7 @@ public Integer call() throws Exception {
             return 1 + 1;
           }
         };
-    assertThat(SpannerRetryHelper.runTxWithRetriesOnAborted(callable), is(equalTo(2)));
+    assertThat(SpannerRetryHelper.runTxWithRetriesOnAborted(callable)).isEqualTo(2);
   }
 
   @Test(expected = IllegalStateException.class)
@@ -190,12 +188,13 @@ public Integer call() throws Exception {
 
   @Test
   public void testExceptionWithRetryInfo() {
+    final int RETRY_DELAY_NANOS = 100_000_000;
     Metadata.Key<RetryInfo> key = ProtoUtils.keyForProto(RetryInfo.getDefaultInstance());
     Status status = Status.fromCodeValue(Status.Code.ABORTED.value());
     Metadata trailers = new Metadata();
     RetryInfo retryInfo =
         RetryInfo.newBuilder()
-            .setRetryDelay(Duration.newBuilder().setNanos(100000000).build())
+            .setRetryDelay(Duration.newBuilder().setNanos(RETRY_DELAY_NANOS).build())
             .build();
     trailers.put(key, retryInfo);
     final SpannerException e =
@@ -214,9 +213,9 @@ public Integer call() throws Exception {
     // The following call should take at least 100ms, as that is the retry delay specified in the
     // retry info of the exception.
     Stopwatch watch = Stopwatch.createStarted();
-    assertThat(SpannerRetryHelper.runTxWithRetriesOnAborted(callable), is(equalTo(2)));
-    long elapsed = watch.elapsed(TimeUnit.MILLISECONDS);
-    assertThat(elapsed >= 100L, is(true));
+    assertThat(SpannerRetryHelper.runTxWithRetriesOnAborted(callable)).isEqualTo(2);
+    long elapsed = watch.elapsed(TimeUnit.NANOSECONDS);
+    assertThat(elapsed >= RETRY_DELAY_NANOS).isTrue();
   }
 
   private SpannerException abortedWithRetryInfo(int nanos) {