test(amber): add unit test coverage for Schedule iterator semantics

amber/src/test/scala/org/apache/texera/amber/engine/architecture/scheduling/ScheduleSpec.scala

@@ -0,0 +1,96 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.texera.amber.engine.architecture.scheduling
+
+import org.apache.texera.amber.core.executor.OpExecInitInfo
+import org.apache.texera.amber.core.virtualidentity.{
+  ExecutionIdentity,
+  OperatorIdentity,
+  PhysicalOpIdentity,
+  WorkflowIdentity
+}
+import org.apache.texera.amber.core.workflow.PhysicalOp
+import org.scalatest.flatspec.AnyFlatSpec
+
+class ScheduleSpec extends AnyFlatSpec {
+
+  private def region(regionId: Long, opId: String): Region = {
+    val physicalOp = PhysicalOp(
+      PhysicalOpIdentity(OperatorIdentity(opId), "main"),
+      WorkflowIdentity(0),
+      ExecutionIdentity(0),
+      OpExecInitInfo.Empty
+    )
+    Region(RegionIdentity(regionId), Set(physicalOp), Set.empty)
+  }
+
+  "Schedule.getRegions" should "return all regions across all levels" in {
+    val r0 = region(0, "a")
+    val r1a = region(1, "b")
+    val r1b = region(2, "c")
+    val schedule = Schedule(Map(0 -> Set(r0), 1 -> Set(r1a, r1b)))
+
+    assert(schedule.getRegions.toSet == Set(r0, r1a, r1b))
+  }
+
+  it should "return an empty list when the schedule is empty" in {
+    assert(Schedule(Map.empty).getRegions.isEmpty)
+  }
+
+  "Schedule" should "iterate level sets in ascending key order starting from the minimum level" in {
+    val r0 = region(0, "a")
+    val r1 = region(1, "b")
+    val r2 = region(2, "c")
+    val schedule = Schedule(Map(1 -> Set(r1), 0 -> Set(r0), 2 -> Set(r2)))
+
+    assert(schedule.toList == List(Set(r0), Set(r1), Set(r2)))
+  }
+
+  it should "report hasNext as false for an empty schedule" in {
+    assert(!Schedule(Map.empty).hasNext)
+  }
+
+  it should "report hasNext as false after the last contiguous level is consumed" in {
+    val schedule = Schedule(Map(0 -> Set(region(0, "a")), 1 -> Set(region(1, "b"))))
+    schedule.next()
+    schedule.next()
+    assert(!schedule.hasNext)
+  }
+
+  it should "stop iteration at the first gap in level keys" in {
+    val r0 = region(0, "a")
+    val rGapped = region(2, "b")
+    val schedule = Schedule(Map(0 -> Set(r0), 2 -> Set(rGapped)))
+
+    assert(schedule.next() == Set(r0))
+    assert(!schedule.hasNext)
+  }
+
+  it should "begin iteration from the minimum level when level keys do not start at zero" in {
+    val r3 = region(3, "a")
+    val r4 = region(4, "b")
+    val schedule = Schedule(Map(3 -> Set(r3), 4 -> Set(r4)))
+
+    assert(schedule.hasNext)
+    assert(schedule.next() == Set(r3))
+    assert(schedule.next() == Set(r4))
+    assert(!schedule.hasNext)
+  }
+}