Add monthly repeat test

app/src/test/java/com/todoroo/astrid/repeats/RepeatMonthlyTests.kt

@@ -55,4 +55,23 @@ class RepeatMonthlyTests : RepeatTests() {
 
         assertEquals(newDayTime(2017, 2, 28, 13, 30), next)
     }
+
+    /* https://tools.ietf.org/html/rfc5545#section-3.3.10
+     * Recurrence rules may generate recurrence instances with an invalid
+     * date (e.g., February 30) or nonexistent local time (e.g., 1:30 AM
+     * on a day where the local time is moved forward by an hour at 1:00
+     * AM).  Such recurrence instances MUST be ignored and MUST NOT be
+     * counted as part of the recurrence set.
+     */
+    @Test
+    fun repeatJanuary30th() {
+        val task = newFromDue(
+                "FREQ=MONTHLY;INTERVAL=1",
+                newDayTime(2017, 1, 30, 13, 30)
+        )
+
+        val next = calculateNextDueDate(task)
+
+        assertEquals(newDayTime(2017, 3, 30, 13, 30), next)
+    }
 }