unit testing for semigroup variants

algebird-test/src/test/scala/com/twitter/algebird/AppendAggregatorTest.scala

@@ -6,16 +6,16 @@ class AppendAggregatorTest extends WordSpec with Matchers {
   val data = Vector.fill(100) { scala.util.Random.nextInt(100) }
   val mpty = Vector.empty[Int]
 
-  // test the methods that appendMonoid method defines or overrides
-  def testMethods[E, M, P](
-    agg1: MonoidAggregator[E, M, P],
-    agg2: MonoidAggregator[E, M, P],
+  // test the methods that appendSemigroup method defines or overrides
+  def testMethodsSemigroup[E, M, P](
+    agg1: Aggregator[E, M, P],
+    agg2: Aggregator[E, M, P],
     data: Seq[E],
     empty: Seq[E]) {
 
     val n = data.length
     val (half1, half2) = data.splitAt(n / 2)
-    val lhs = agg1.appendAll(half1)
+    val lhs = agg1.appendAll(agg1.prepare(half1.head), half1.tail)
 
     data.foreach { e =>
       agg1.prepare(e) should be(agg2.prepare(e))
@@ -24,7 +24,6 @@ class AppendAggregatorTest extends WordSpec with Matchers {
     agg1.present(lhs) should be(agg2.present(lhs))
 
     agg1(data) should be (agg2(data))
-    agg1(empty) should be (agg2(empty))
 
     agg1.applyOption(data) should be(agg2.applyOption(data))
     agg1.applyOption(empty) should be(agg2.applyOption(empty))
@@ -34,15 +33,26 @@ class AppendAggregatorTest extends WordSpec with Matchers {
     }
 
     agg1.appendAll(lhs, half2) should be(agg2.appendAll(lhs, half2))
+  }
+
+  // test the methods that appendMonoid method defines or overrides
+  def testMethodsMonoid[E, M, P](
+    agg1: MonoidAggregator[E, M, P],
+    agg2: MonoidAggregator[E, M, P],
+    data: Seq[E],
+    empty: Seq[E]) {
 
-    agg2.appendAll(data) should be(agg2.appendAll(data))
+    testMethodsSemigroup(agg1, agg2, data, empty)
+
+    agg1(empty) should be (agg2(empty))
+    agg1.appendAll(data) should be(agg2.appendAll(data))
   }
 
   "appendMonoid" should {
     "be equivalent to integer monoid aggregator" in {
       val agg1 = Aggregator.fromMonoid[Int]
       val agg2 = Aggregator.appendMonoid((m: Int, e: Int) => m + e)
-      testMethods(agg1, agg2, data, mpty)
+      testMethodsMonoid(agg1, agg2, data, mpty)
     }
 
     "be equivalent to set monoid aggregator" in {
@@ -54,7 +64,26 @@ class AppendAggregatorTest extends WordSpec with Matchers {
       val agg1 = Aggregator.prepareMonoid((e: Int) => Set(e))(setMonoid)
       val agg2 = Aggregator.appendMonoid((m: Set[Int], e: Int) => m + e)(setMonoid)
 
-      testMethods(agg1, agg2, data, mpty)
+      testMethodsMonoid(agg1, agg2, data, mpty)
+    }
+  }
+
+  "appendSemigroup" should {
+    "be equivalent to integer semigroup aggregator" in {
+      val agg1 = Aggregator.fromSemigroup[Int]
+      val agg2 = Aggregator.appendSemigroup(identity[Int]_, (m: Int, e: Int) => m + e)
+      testMethodsSemigroup(agg1, agg2, data, mpty)
+    }
+
+    "be equivalent to set semigroup aggregator" in {
+      object setSemigroup extends Semigroup[Set[Int]] {
+        def plus(m1: Set[Int], m2: Set[Int]) = m1 ++ m2
+      }
+
+      val agg1 = Aggregator.prepareSemigroup((e: Int) => Set(e))(setSemigroup)
+      val agg2 = Aggregator.appendSemigroup((e: Int) => Set(e), (m: Set[Int], e: Int) => m + e)(setSemigroup)
+
+      testMethodsSemigroup(agg1, agg2, data, mpty)
     }
   }
 }