RUBY-2447 Fix intermittent transaction examples test failures (#2135)

* run tx examples first

* add diagnostics to transaction aborts

* try majority read/write concerns

* flush router config to work around SERVER-53015

Co-authored-by: Oleg Pudeyev <oleg@bsdpower.com>

Author: p-mongo

Rakefile

@@ -32,8 +32,9 @@ CLASSIFIERS = [
   [%r,^spec_tests,, :spec],
 ]
 
-RUN_PRIORITY = %i(unit
+RUN_PRIORITY = %i(
   tx_examples
+  unit
   integration sdam_integration cursor_reaping query_cache
   spec spec_sdam_integration
 )

lib/mongo/session.rb

@@ -379,6 +379,7 @@ def with_transaction(options=nil)
           rv = yield self
         rescue Exception => e
           if within_states?(STARTING_TRANSACTION_STATE, TRANSACTION_IN_PROGRESS_STATE)
+            log_warn("Aborting transaction due to #{e.class}: #{e}")
             abort_transaction
             transaction_in_progress = false
           end
@@ -443,7 +444,7 @@ def with_transaction(options=nil)
       true
     ensure
       if transaction_in_progress
-        log_warn('with_transaction callback altered with_transaction loop, aborting transaction')
+        log_warn('with_transaction callback broke out of with_transaction loop, aborting transaction')
         begin
           abort_transaction
         rescue Error::OperationFailure, Error::InvalidTransactionOperation

spec/integration/transactions_examples_spec.rb

@@ -4,28 +4,42 @@
   require_wired_tiger
   require_transaction_support
 
+  let(:client) do
+    authorized_client.with(read_concern: {level: :majority}, write: {w: :majority})
+  end
+
   let(:hr) do
-    authorized_client.use(:hr).database
+    client.use(:hr).database
   end
 
   let(:reporting) do
-    authorized_client.use(:reporting).database
+    client.use(:reporting).database
   end
 
   before(:each) do
     hr[:employees].insert_one(employee: 3, status: 'Active')
+
+    # Sanity check since this test likes to fail
+    employee = hr[:employees].find({ employee: 3 }, limit: 1).first
+    expect(employee).to_not be_nil
+
     reporting[:events].insert_one(employee: 3, status: { new: 'Active', old: nil})
   end
 
   after(:each) do
     hr.drop
     reporting.drop
+
+    # Work around https://jira.mongodb.org/browse/SERVER-53015
+    ::Utils.mongos_each_direct_client do |client|
+      client.database.command(flushRouterConfig: 1)
+    end
   end
 
   context 'individual examples' do
 
     let(:session) do
-      authorized_client.start_session
+      client.start_session
     end
 
     # Start Transactions Intro Example 1
@@ -142,10 +156,6 @@ def commit_with_retry(session)
 
   context 'Transactions Retry Example 3 (combined example)' do
 
-    let(:client) do
-      authorized_client
-    end
-
     let(:run_transaction) do
 
       # Start Transactions Retry Example 3