test: fix flaky InlineBeginTransactionTest (#664)

The query_ThenUpdate_ThenConsumeResultSet did not take into account that the session pool
initialization will execute 4 BatchCreateSessions requests. These will normally be executed
before the test transaction, but sometimes at least one of those requests might arrive after
the transaction has started. That could cause the last 3 requests on the mock server to be
different from what the test expected.

Author: olavloite

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

@@ -1248,14 +1248,13 @@ public Long run(TransactionContext transaction) throws Exception {
     // id returned by the update.
     assertThat(mockSpanner.countRequestsOfType(BeginTransactionRequest.class)).isEqualTo(0L);
     assertThat(mockSpanner.countRequestsOfType(ExecuteSqlRequest.class)).isEqualTo(2L);
+    assertThat(mockSpanner.countRequestsOfType(CommitRequest.class)).isEqualTo(1L);
     assertThat(countTransactionsStarted()).isEqualTo(1);
-    List<AbstractMessage> requests = mockSpanner.getRequests();
-    requests = requests.subList(requests.size() - 3, requests.size());
+    List<AbstractMessage> requests = mockSpanner.getRequestsOfType(ExecuteSqlRequest.class);
     assertThat(requests.get(0)).isInstanceOf(ExecuteSqlRequest.class);
     assertThat(((ExecuteSqlRequest) requests.get(0)).getSql()).isEqualTo(UPDATE_STATEMENT.getSql());
     assertThat(requests.get(1)).isInstanceOf(ExecuteSqlRequest.class);
     assertThat(((ExecuteSqlRequest) requests.get(1)).getSql()).isEqualTo(SELECT1.getSql());
-    assertThat(requests.get(2)).isInstanceOf(CommitRequest.class);
   }
 
   private int countRequests(Class<? extends AbstractMessage> requestType) {

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

@@ -1905,6 +1905,20 @@ public List<AbstractMessage> getRequests() {
     return new ArrayList<>(this.requests);
   }
 
+  public void clearRequests() {
+    this.requests.clear();
+  }
+
+  public List<AbstractMessage> getRequestsOfType(Class<? extends AbstractMessage> type) {
+    List<AbstractMessage> res = new ArrayList<>();
+    for (AbstractMessage m : this.requests) {
+      if (m.getClass().equals(type)) {
+        res.add(m);
+      }
+    }
+    return res;
+  }
+
   public Iterable<Class<? extends AbstractMessage>> getRequestTypes() {
     List<Class<? extends AbstractMessage>> res = new LinkedList<>();
     for (AbstractMessage m : this.requests) {