diff --git a/src/resource_interval.rs b/src/resource_interval.rs
index 9c1d4ff..2c0d049 100644
--- a/src/resource_interval.rs
+++ b/src/resource_interval.rs
@@ -13,7 +13,14 @@ impl ResourceInterval {
         ResourceInterval(HashMap::new())
     }
 
-    pub fn insert(&mut self, other: ResourceInterval) {
+    pub fn insert(&mut self, resource: &Resource, intervals: &IntervalSet) {
+        self.0
+            .entry(resource.clone())
+            .or_insert(IntervalSet::new())
+            .merge(intervals);
+    }
+
+    pub fn union(&mut self, other: ResourceInterval) {
         for (res, is) in other.iter() {
             self.0
                 .entry(res.clone())
@@ -22,7 +29,7 @@ impl ResourceInterval {
         }
     }
 
-    pub fn remove(&mut self, other: ResourceInterval) {
+    pub fn subtract(&mut self, other: ResourceInterval) {
         for (res, is) in other.iter() {
             let avail = self.0.entry(res.clone()).or_insert(IntervalSet::new());
             *avail = avail.difference(is);
diff --git a/src/task.rs b/src/task.rs
index 009d43c..33fbefa 100644
--- a/src/task.rs
+++ b/src/task.rs
@@ -68,7 +68,7 @@ impl TaskDefinition {
             requires: self.requires.clone(),
 
             schedule: schedule,
-            valid_over: IntervalSet::from(vec![Interval::new(start, actual_end)]),
+            valid_over: IntervalSet::from(Interval::new(start, actual_end)),
             timezone: self.timezone,
         }
     }
@@ -293,5 +293,13 @@ mod tests {
                 panic!("{:?}", e);
             }
         };
+
+        // Ensure that the intervals generated over the valid period
+        // exactly cover the valid period
+        let mut theoretical = ResourceInterval::new();
+        theoretical.insert(&"resource_a".to_owned(), &task.valid_over);
+        theoretical.insert(&"resource_b".to_owned(), &task.valid_over);
+        let generated = IntervalSet::from(task.generate_intervals(&theoretical).unwrap());
+        assert_eq!(task.valid_over, generated);
     }
 }