SERVER-31409 Create basic multi-version rollback Javascript test

2 files changed, 84 insertions, 4 deletions

diff --git a/src/mongo/shell/replsettest.js b/src/mongo/shell/replsettest.js
index 94a4194eafd..c696e102cf4 100644
--- a/src/mongo/shell/replsettest.js
+++ b/src/mongo/shell/replsettest.js
@@ -725,6 +725,29 @@ var ReplSetTest = function(opts) {
         return this.getSecondaries(timeout)[0];
     };
 
+    this.getArbiters = function() {
+        var arbiters = [];
+        for (var i = 0; i < this.nodes.length; i++) {
+            var node = this.nodes[i];
+
+            let isArbiter = false;
+
+            assert.retryNoExcept(() => {
+                isArbiter = node.getDB('admin').isMaster('admin').arbiterOnly;
+                return true;
+            }, `Could not call 'isMaster' on ${node}.`, 3, 1000);
+
+            if (isArbiter) {
+                arbiters.push(node);
+            }
+        }
+        return arbiters;
+    };
+
+    this.getArbiter = function() {
+        return this.getArbiters()[0];
+    };
+
     this.status = function(timeout) {
         var master = _callIsMaster();
         if (!master) {
@@ -1982,6 +2005,13 @@ var ReplSetTest = function(opts) {
     };
 
     /**
+     * Returns whether or not this ReplSetTest uses mongobridge.
+     */
+    this.usesBridge = function() {
+        return _useBridge;
+    };
+
+    /**
      * Wait for a state indicator to go to a particular state or states.
      *
      * @param node is a single node or list of nodes, by id or conn
diff --git a/src/mongo/shell/servers.js b/src/mongo/shell/servers.js
index 6d6390567d9..ebe96ab57bd 100644
--- a/src/mongo/shell/servers.js
+++ b/src/mongo/shell/servers.js
@@ -94,6 +94,7 @@ var MongoRunner, _startMongod, startMongoProgram, runMongoProgram, startMongoPro
     var convertVersionStringToArray = function(versionString) {
         assert("" !== versionString, "Version strings must not be empty");
         var versionArray = versionString.split('.');
+
         assert.gt(versionArray.length,
                   1,
                   "MongoDB versions must have at least two components to compare, but \"" +
@@ -150,23 +151,72 @@ var MongoRunner, _startMongod, startMongoProgram, runMongoProgram, startMongoPro
 
     /**
      * Returns true if two version strings could represent the same version. This is true
-     * if, after passing the versions through getBinVersionFor, the the versions have the
+     * if, after passing the versions through getBinVersionFor, the versions have the
      * same value for each version component up through the length of the shorter version.
      *
      * That is, 3.2.4 compares equal to 3.2, but 3.2.4 does not compare equal to 3.2.3.
      */
     MongoRunner.areBinVersionsTheSame = function(versionA, versionB) {
 
+        // Check for invalid version strings first.
+        convertVersionStringToArray(MongoRunner.getBinVersionFor(versionA));
+        convertVersionStringToArray(MongoRunner.getBinVersionFor(versionB));
+
+        try {
+            return (0 === MongoRunner.compareBinVersions(versionA, versionB));
+        } catch (err) {
+            // compareBinVersions() throws an error if two versions differ only by the git hash.
+            return false;
+        }
+    };
+
+    /**
+     * Compares two version strings and returns:
+     *      1, if the first is more recent
+     *      0, if they are equal
+     *     -1, if the first is older
+     *
+     * Note that this function only compares up to the length of the shorter version.
+     * Because of this, minor versions will compare equal to the major versions they stem
+     * from, but major-major and minor-minor version pairs will undergo strict comparison.
+     */
+    MongoRunner.compareBinVersions = function(versionA, versionB) {
+
+        let stringA = versionA;
+        let stringB = versionB;
+
         versionA = convertVersionStringToArray(MongoRunner.getBinVersionFor(versionA));
         versionB = convertVersionStringToArray(MongoRunner.getBinVersionFor(versionB));
 
+        // Treat the githash as a separate element, if it's present.
+        versionA.push(...versionA.pop().split("-"));
+        versionB.push(...versionB.pop().split("-"));
+
         var elementsToCompare = Math.min(versionA.length, versionB.length);
+
         for (var i = 0; i < elementsToCompare; ++i) {
-            if (versionA[i] != versionB[i]) {
-                return false;
+            var elementA = versionA[i];
+            var elementB = versionB[i];
+
+            if (elementA === elementB) {
+                continue;
+            }
+
+            var numA = parseInt(elementA);
+            var numB = parseInt(elementB);
+
+            assert(!isNaN(numA) && !isNaN(numB), "Cannot compare non-equal non-numeric versions.");
+
+            if (numA > numB) {
+                return 1;
+            } else if (numA < numB) {
+                return -1;
             }
+
+            assert(false, `Unreachable case. Provided versions: {${stringA}, ${stringB}}`);
         }
-        return true;
+
+        return 0;
     };
 
     MongoRunner.logicalOptions = {