DRIVERS-720 Add unified tests for LB support (#958)

Author: Divjot Arora

source/load-balancers/tests/README.rst

@@ -0,0 +1,68 @@
+===========================
+Load Balancer Support Tests
+===========================
+
+.. contents::
+
+----
+
+Introduction
+============
+
+This document describes how drivers should create load balanced clusters for
+testing and how tests should be executed for such clusters.
+
+Testing Requirements
+====================
+
+For each server version that supports load balanced clusters, drivers MUST
+add two Evergreen tasks: one with a sharded cluster with both authentication
+and TLS enabled and one with a sharded cluster with authentication and TLS
+disabled. In each task, the sharded cluster MUST be configured with two
+mongos nodes running on localhost ports 27017 and 27018. The shard and config
+servers may run on any free ports. Each task MUST also start up two TCP load
+balancers operating in round-robin mode: one fronting both mongos servers and
+one fronting a single mongos.
+
+Load Balancer Configuration
+---------------------------
+
+Drivers MUST use the ``run-load-balancer.sh`` script in
+``drivers-evergreen-tools`` to start the TCP load balancers for Evergreen
+tasks. This script MUST be run after the backing sharded cluster has already
+been started. The script writes the URIs of the load balancers to a YAML
+expansions file, which can be read by drivers via the ``expansions.update``
+Evergreen command. This will store the URIs into the ``SINGLE_MONGOS_LB_URI``
+and ``MULTI_MONGOS_LB_URI`` environment variables.
+
+Test Runner Configuration
+-------------------------
+
+If the backing sharded cluster is configured with TLS enabled, drivers MUST
+add the relevant TLS options to both ``SINGLE_MONGOS_LB_URI`` and
+``MULTI_MONGOS_LB_URI`` to ensure that test clients can connect to the
+cluster. Drivers MUST use the final URI stored in ``SINGLE_MONGOS_LB_URI``
+(with additional TLS options if required) to configure internal clients for
+test runners (e.g. the internal MongoClient described by the `Unified Test
+Format spec <../../unified-test-format/unified-test-format.rst>`__).
+
+In addition to modifying load balancer URIs, drivers MUST also mock server
+support for returning a ``serviceId`` field in ``hello`` or legacy ``hello``
+command responses when running tests against a load-balanced cluster. This
+can be done by using the value of ``topologyVersion.processId`` to set
+``serviceId``. This MUST be done for all connections established by the test
+runner, including those made by any internal clients.
+
+Tests
+======
+
+The YAML and JSON files in this directory contain platform-independent tests
+written in the `Unified Test Format
+<../../unified-test-format/unified-test-format.rst>`_. Drivers MUST run the
+following test suites against a load balanced cluster:
+
+#. All test suites written in the Unified Test Format
+#. Retryable Reads
+#. Retryable Writes
+#. Change Streams
+#. Initial DNS Seedlist Discovery