fix up prev-button tests

tests/toolbar/prev-button.js

@@ -8,8 +8,7 @@ SEE ALSO:
 describe('prev button', function() {
 	pushOptions({
 		defaultView: 'agendaWeek',
-		defaultDate: '2017-06-08',
-		dateIncrement: { years: 1 } // prev range is 2016-06-05 - 2016-06-12
+		defaultDate: '2017-06-08'
 	});
 
 	describe('when there is no specified validRange', function() {
@@ -21,7 +20,8 @@ describe('prev button', function() {
 
 	describe('when prev date range is completely before validRange', function() {
 		pushOptions({
-			validRange: { start: '2018-06-12' }
+			validRange: { start: '2018-06-12' },
+			dateIncrement: { years: 1 } // prev range is 2016-06-05 - 2016-06-12
 		});
 		it('is disabled', function() {
 			initCalendar();
@@ -33,7 +33,8 @@ describe('prev button', function() {
 		pushOptions({
 			defaultView: 'month',
 			defaultDate: '2017-03-01',
-			validRange: { start: '2017-02-07' }
+			validRange: { start: '2017-02-07' },
+			dateIncrement: { years: 1 } // prev range is 2016-06-05 - 2016-06-12
 		});
 
 		it('when prev date range is partially before validRange', function() {
@@ -46,7 +47,8 @@ describe('prev button', function() {
 		pushOptions({
 			defaultDate: '2017-03-27',
 			defaultView: 'basicDay',
-			weekends: false
+			weekends: false,
+			dateIncrement: { years: 1 } // prev range is 2016-06-05 - 2016-06-12
 		});
 		it('is enabled', function() {
 			initCalendar();
@@ -54,11 +56,11 @@ describe('prev button', function() {
 		});
 	});
 
-	describe('when date range is between two weeks', function() {
+	describe('when defaultDate is constrained backward to validRange and prev week is valid', function() {
 		pushOptions({
-			defaultDate: '2017-05-29',
+			defaultDate: '2017-07-17',
 			defaultView: 'agendaWeek',
-			validRange: { start: '2017-05-24', end: '2017-05-30' }
+			validRange: { start: '2017-03-20', end: '2017-03-30' }
 		});
 		it('is enabled', function() {
 			initCalendar();