chore(spanner): fix code and tests

[harshachinta]

No description provided.

[harshachinta]

Removing this unit test since it is not possible to change the txnstate to ABORTED of the TransactionManager using unit tests. This is needed since we are calling resetForRetryAsync, which will fail if transactionstate is not ABORTED.

We have same tests covered in mock spanner

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

Line 75 in c8d1e63

public class MultiplexedSessionDatabaseClientMockServerTest extends AbstractMockServerTest {

[olavloite]

nit: do we really need this check? (and if so, could we change is to !mutations.isEmpty())

[harshachinta]

I noticed that at this point, there are no mutations to commit, making the db.write call unnecessary. Adding a check for pending mutations before committing will avoid an unnecessary backend call and save some time in our tests, though the improvement is minimal.