CSHARP-3891: Add a load balancer test case for SRV resolving to 0 hosts. (#680)

Author: DmitryLukyanov

tests/MongoDB.Driver.Core.Tests/Specifications/initial-dns-seedlist-discovery/tests/load-balanced/loadBalanced-directConnection.yml

@@ -0,0 +1,13 @@
+# The TXT record for test20.test.build.10gen.cc contains loadBalanced=true.
+# DRIVERS-1721 introduced this test as passing.
+uri: "mongodb+srv://test20.test.build.10gen.cc/?directConnection=false"
+seeds:
+    - localhost.test.build.10gen.cc:27017
+hosts:
+    # In LB mode, the driver does not do server discovery, so the hostname does
+    # not get resolved to localhost:27017.
+    - localhost.test.build.10gen.cc:27017
+options:
+    loadBalanced: true
+    ssl: true
+    directConnection: false

tests/MongoDB.Driver.Core.Tests/Specifications/initial-dns-seedlist-discovery/tests/load-balanced/loadBalanced-no-results.json

@@ -0,0 +1,7 @@
+{
+  "uri": "mongodb+srv://test4.test.build.10gen.cc/?loadBalanced=true",
+  "seeds": [],
+  "hosts": [],
+  "error": true,
+  "comment": "Should fail because no SRV records are present for this URI."
+}

tests/MongoDB.Driver.Core.Tests/Specifications/initial-dns-seedlist-discovery/tests/load-balanced/loadBalanced-no-results.yml

@@ -0,0 +1,5 @@
+uri: "mongodb+srv://test4.test.build.10gen.cc/?loadBalanced=true"
+seeds: []
+hosts: []
+error: true
+comment: Should fail because no SRV records are present for this URI.

tests/MongoDB.Driver.Core.Tests/Specifications/initial-dns-seedlist-discovery/tests/load-balanced/loadBalanced-replicaSet-errors.yml

@@ -0,0 +1,6 @@
+# The TXT record for test20.test.build.10gen.cc contains loadBalanced=true.
+uri: "mongodb+srv://test20.test.build.10gen.cc/?replicaSet=replset"
+seeds: []
+hosts: []
+error: true
+comment: Should fail because loadBalanced=true is incompatible with replicaSet

tests/MongoDB.Driver.Core.Tests/Specifications/initial-dns-seedlist-discovery/tests/load-balanced/loadBalanced-true-multiple-hosts.yml

@@ -0,0 +1,5 @@
+uri: "mongodb+srv://test1.test.build.10gen.cc/?loadBalanced=true"
+seeds: []
+hosts: []
+error: true
+comment: Should fail because loadBalanced is true but the SRV record resolves to multiple hosts

tests/MongoDB.Driver.Core.Tests/Specifications/initial-dns-seedlist-discovery/tests/load-balanced/loadBalanced-true-txt.yml

@@ -0,0 +1,10 @@
+uri: "mongodb+srv://test20.test.build.10gen.cc/"
+seeds:
+    - localhost.test.build.10gen.cc:27017
+hosts:
+    # In LB mode, the driver does not do server discovery, so the hostname does
+    # not get resolved to localhost:27017.
+    - localhost.test.build.10gen.cc:27017
+options:
+    loadBalanced: true
+    ssl: true