chore: fix session acquire timeout test (#2793)

* chore: fix session acquire timeout test

The test for session acquire timeout did not actually do what it
was supposed to do, as it did not check that a timeout was actually
registered. This again also caused it to busy-wait for 5 seconds
to times (MinSessions=0 and MinSessions=1). This fixes both the
actual test, and reduces the overall test time by about 10 seconds.

* chore: address review comments

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

@@ -1166,8 +1166,8 @@ public void blockAndTimeoutOnPoolExhaustion() throws Exception {
     latch.await();
     // Wait until the request has timed out.
     int waitCount = 0;
-    while (pool.getNumWaiterTimeouts() == 0L && waitCount < 1000) {
-      Thread.sleep(5L);
+    while (pool.getNumWaiterTimeouts() == 0L && waitCount < 5000) {
+      Thread.sleep(1L);
       waitCount++;
     }
     // Return the checked out session to the pool so the async request will get a session and
@@ -1214,8 +1214,8 @@ public void blockAndTimeoutOnPoolExhaustion_withAcquireSessionTimeout() throws E
     latch.await();
     // Wait until the request has timed out.
     int waitCount = 0;
-    while (pool.getNumWaiterTimeouts() == 0L && waitCount < 1000) {
-      Thread.sleep(5L);
+    while (pool.getNumWaiterTimeouts() == 0L && waitCount < 5000) {
+      Thread.sleep(1L);
       waitCount++;
     }
     // Return the checked out session to the pool so the async request will get a session and
@@ -1639,15 +1639,16 @@ public void testSessionNotFoundPartitionedUpdate() {
     assertThat(impl.executePartitionedUpdate(statement)).isEqualTo(1L);
   }
 
+  @SuppressWarnings("rawtypes")
   @Test
   public void testSessionMetrics() throws Exception {
     // Create a session pool with max 2 session and a low timeout for waiting for a session.
     options =
         SessionPoolOptions.newBuilder()
             .setMinSessions(1)
             .setMaxSessions(2)
-            .setMaxIdleSessions(0)
             .setInitialWaitForSessionTimeoutMillis(50L)
+            .setAcquireSessionTimeout(null)
             .build();
     FakeClock clock = new FakeClock();
     clock.currentTimeMillis.set(System.currentTimeMillis());
@@ -1746,10 +1747,12 @@ public void testSessionMetrics() throws Exception {
     latch.await();
     // Wait until the request has timed out.
     int waitCount = 0;
-    while (pool.getNumWaiterTimeouts() == 0L && waitCount < 1000) {
-      Thread.sleep(5L);
+    while (pool.getNumWaiterTimeouts() == 0L && waitCount < 5000) {
+      //noinspection BusyWait
+      Thread.sleep(1L);
       waitCount++;
     }
+    assertTrue(pool.getNumWaiterTimeouts() > 0L);
     // Return the checked out session to the pool so the async request will get a session and
     // finish.
     session2.close();