Added prose test

Author: papafe

specifications/sessions/tests/snapshot-sessions.json

@@ -1061,6 +1061,24 @@
             }
           ]
         },
+        {
+          "name": "find",
+          "object": "collection0",
+          "arguments": {
+            "session": "session2",
+            "filter": {}
+          },
+          "expectResult": [
+            {
+              "_id": 1,
+              "x": 11
+            },
+            {
+              "_id": 2,
+              "x": 11
+            }
+          ]
+        },
         {
           "name": "find",
           "object": "collection0",
@@ -1115,6 +1133,20 @@
                 "databaseName": "database0"
               }
             },
+            {
+              "commandStartedEvent": {
+                "command": {
+                  "find": "collection0",
+                  "readConcern": {
+                    "level": "snapshot",
+                    "atClusterTime": {
+                      "$$matchesEntity": "savedSnapshotTime"
+                    }
+                  }
+                },
+                "databaseName": "database0"
+              }
+            },
             {
               "commandStartedEvent": {
                 "command": {

specifications/sessions/tests/snapshot-sessions.yml

@@ -378,7 +378,7 @@ tests:
       fieldName: x
       filter: {}
       session: session0
-    expectResult: [ 11 ] 
+    expectResult: [ 11 ]
   expectEvents:
   - client: client0
     events:
@@ -508,6 +508,16 @@ tests:
               sessionOptions:
                 snapshot: true
                 snapshotTime: *savedSnapshotTime
+    - name: find
+      object: collection0
+      arguments:
+        session: session2
+        filter: {}
+      expectResult:
+        - { _id: 1, x: 11 }
+        - { _id: 2, x: 11 }
+    ## Calling find again to verify that atClusterTime/snapshotTime has not been modified after the first query
+    ## as it would happen if snapshotTime had not been specified
     - name: find
       object: collection0
       arguments:
@@ -540,7 +550,14 @@ tests:
               find: collection0
               readConcern:
                 level: snapshot
-                atClusterTime: { $$matchesEntity: savedSnapshotTime }
+                atClusterTime: { $$matchesEntity: *savedSnapshotTime }
+            databaseName: database0
+        - commandStartedEvent:
+            command:
+              find: collection0
+              readConcern:
+                level: snapshot
+                atClusterTime: { $$matchesEntity: *savedSnapshotTime }
             databaseName: database0
         - commandStartedEvent:
             command:

src/MongoDB.Driver/MongoClient.cs

@@ -622,12 +622,18 @@ private RenderArgs<BsonDocument> GetRenderArgs()
 
         private IClientSessionHandle StartSession(ClientSessionOptions options)
         {
-            if (options != null && options.Snapshot && options.CausalConsistency == true)
+            if (options != null)
             {
-                throw new NotSupportedException("Combining both causal consistency and snapshot options is not supported.");
-            }
+                if (options.SnapshotTime != null && !options.Snapshot)
+                {
+                    throw new NotSupportedException("Specifying a snapshot time requires snapshot to be true.");
+                }
 
-            //TODO Throw an exception if SnapshotTime is set and Snapshot is not true.
+                if (options.Snapshot && options.CausalConsistency == true)
+                {
+                    throw new NotSupportedException("Combining both causal consistency and snapshot options is not supported.");
+                }
+            }
 
             options ??= new ClientSessionOptions();
             if (_settings.Timeout.HasValue && options.DefaultTransactionOptions?.Timeout == null)

tests/MongoDB.Driver.Tests/Specifications/sessions/SessionsProseTests.cs

@@ -357,6 +357,24 @@ public void Ensure_cluster_times_are_not_gossiped_on_SDAM_commands()
             commandStartedEvents[0].Command["$clusterTime"].Should().Be(clusterTime);
         }
 
+        [Fact]
+        public void If_SnapshotTime_is_set_Snapshot_must_be_true()
+        {
+            RequireServer.Check();
+
+            var sessionOptions = new ClientSessionOptions
+            {
+                Snapshot = false,
+                SnapshotTime = new BsonTimestamp(1, 1)
+            };
+
+            var mongoClient = DriverTestConfiguration.Client;
+
+            var exception = Record.Exception(() => mongoClient.StartSession(sessionOptions));
+            exception.Should().BeOfType<NotSupportedException>();
+        }
+
+
         private sealed class MongocryptdContext : IDisposable
         {
             public IMongoClient MongoClient { get; }