commit a8017e90c767c2e8c7ca82f95d4cdee41a0705ee
Author: Charlie Swanson <charlie.swanson@mongodb.com>
Date:   Wed Sep 11 13:40:18 2019 -0400

    WIP towards SERVER-43287

diff --git a/jstests/aggregation/extras/utils.js b/jstests/aggregation/extras/utils.js
index 7364ecde54..fd5752df00 100644
--- a/jstests/aggregation/extras/utils.js
+++ b/jstests/aggregation/extras/utils.js
@@ -357,3 +357,10 @@ function generateCollection({
     assert.eq(numDocs, res.nInserted);
     assert.eq(numDocs, coll.find().itcount());
 }
+
+/**
+ * Asserts that 'coll' exists.
+ */
+function collectionExists(coll) {
+    return Array.contains(coll.getDB().getCollectionNames(), coll.getName());
+}
diff --git a/jstests/aggregation/no_output_to_system.js b/jstests/aggregation/no_output_to_system.js
new file mode 100644
index 0000000000..3b323ef79e
--- /dev/null
+++ b/jstests/aggregation/no_output_to_system.js
@@ -0,0 +1,18 @@
+// Tests that you cannot use aggregation to output to a system collection.
+(function() {
+"use strict";
+
+load('jstests/aggregation/extras/utils.js');  // For 'assertErrorCode'.
+
+const input = db.no_output_to_system;
+input.drop();
+assert.commandWorked(input.insert({_id: 0}));
+
+// ensure we cant do dangerous things to system collections
+const outputInSystem = db.system.no_output_to_system;
+assertErrorCode(input, {$out: outputInSystem.getName()}, 17385);
+assert(!collectionExists(outputInSystem));
+
+assertErrorCode(input, {$merge: outputInSystem.getName()}, 17385);
+assert(!collectionExists(outputInSystem));
+}());
diff --git a/jstests/aggregation/bugs/server3253.js b/jstests/aggregation/sources/out/basic_functionality.js
similarity index 79%
rename from jstests/aggregation/bugs/server3253.js
rename to jstests/aggregation/sources/out/basic_functionality.js
index 5df6736e88..e5fa6bfd94 100644
--- a/jstests/aggregation/bugs/server3253.js
+++ b/jstests/aggregation/sources/out/basic_functionality.js
@@ -1,3 +1,4 @@
+// Basic tests for the $out stage.
 // Cannot implicitly shard accessed collections because unsupported use of sharded collection
 // for output collection of aggregation pipeline.
 // @tags: [
@@ -5,21 +6,19 @@
 //   assumes_unsharded_collection,
 // ]
 
-// server-3253 Unsharded support for $out
+(function() {
+"use strict";
 load('jstests/aggregation/extras/utils.js');
 
-var input = db.server3253_in;
-var inputDoesntExist = db.server3253_doesnt_exist;
-var output = db.server3253_out;
-var cappedOutput = db.server3253_out_capped;
+const input = db.server3253_in;
+const inputDoesntExist = db.server3253_doesnt_exist;
+const output = db.server3253_out;
+const cappedOutput = db.server3253_out_capped;
 
 input.drop();
 inputDoesntExist.drop();  // never created
 output.drop();
-
-function collectionExists(coll) {
-    return Array.contains(coll.getDB().getCollectionNames(), coll.getName());
-}
+cappedOutput.drop();
 
 function getOutputIndexes() {
     return output.getIndexes().sort(function(a, b) {
@@ -53,14 +52,12 @@ function listCollections(name) {
     return new DBCommandCursor(db, collectionInfosCursor).toArray();
 }
 
-input.insert({_id: 1});
-input.insert({_id: 2});
-input.insert({_id: 3});
+assert.commandWorked(input.insert([{_id: 1}, {_id: 2}, {_id: 3}]));
 
-// insert into output so that the index exists and test() does not fail the first time around
+// Insert into output so that the index exists and test() does not fail the first time around.
 output.insert({_id: 1});
 
-// ensure there are no tmp agg_out collections before we begin
+// Ensure there are no tmp agg_out collections before we begin.
 assert.eq([], listCollections(/tmp\.agg_out/));
 
 // basic test
@@ -104,10 +101,6 @@ if (jsTest.options().storageEngine !== "mobile") {
 // ensure everything works even if input doesn't exist.
 test(inputDoesntExist, [], []);
 
-// ensure we cant do dangerous things to system collections
-var outputInSystem = db.system.server3253_out;
-assertErrorCode(input, {$out: outputInSystem.getName()}, 17385);
-assert(!collectionExists(outputInSystem));
-
 // shoudn't leave temp collections laying around
 assert.eq([], listCollections(/tmp\.agg_out/));
+}());