Adds driveOnScheduler to enable using custom mock scheduler with Driver.

RxCocoa/Common/CocoaUnits/Driver/Driver+Operators.swift

@@ -147,7 +147,7 @@ extension DriverConvertibleType {
     - returns: An observable sequence whose events are printed to standard output.
     */
     @warn_unused_result(message="http://git.io/rxs.uo")
-    public func debug(identifier: String? = nil, file: String = __FILE__, line: Int = __LINE__, function: String = __FUNCTION__) -> Driver<E> {
+    public func debug(identifier: String? = nil, file: String = __FILE__, line: UInt = __LINE__, function: String = __FUNCTION__) -> Driver<E> {
         let source = self.asObservable()
             .debug(identifier, file: file, line: line, function: function)
         return Driver(source)

RxCocoa/Common/CocoaUnits/Driver/Driver.swift

@@ -166,5 +166,26 @@ public struct Drive {
     
 }
 
+/**
+ This method can be used in unit tests to ensure that driver is using mock schedulers instead of 
+ maind schedulers.
+ 
+ To be able to use it, please import RxCocoa using testable attribute
+ 
+    @testable import RxCocoa
+*/
+func driveOnScheduler(scheduler: SchedulerType, action: () -> ()) {
+    let originalObserveOnScheduler = driverObserveOnScheduler
+    let originalSubscribeOnScheduler = driverSubscribeOnScheduler
+
+    driverObserveOnScheduler = scheduler
+    driverSubscribeOnScheduler = scheduler
+
+    action()
+
+    driverObserveOnScheduler = originalObserveOnScheduler
+    driverSubscribeOnScheduler = originalSubscribeOnScheduler
+}
+
 var driverObserveOnScheduler: SchedulerType = MainScheduler.instance
 var driverSubscribeOnScheduler: SchedulerType = ConcurrentMainScheduler.instance

RxCocoa/Common/CocoaUnits/Driver/Variable+Driver.swift

@@ -0,0 +1,26 @@
+//
+//  Variable+Driver.swift
+//  Rx
+//
+//  Created by Krunoslav Zaher on 12/28/15.
+//  Copyright © 2015 Krunoslav Zaher. All rights reserved.
+//
+
+import Foundation
+#if !RX_NO_MODULE
+    import RxSwift
+#endif
+
+extension Variable {
+    /**
+     Converts `Variable` to `Driver` unit.
+
+     - returns: Driving observable sequence.
+     */
+    @warn_unused_result(message="http://git.io/rxs.uo")
+    public func asDriver() -> Driver<E> {
+        let source = self
+            .observeOn(driverObserveOnScheduler)
+        return Driver(source)
+    }
+}