Add graph summation "+" to DiGraph (#744)

* Add DiGraph sum and DiGraph sum test

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@ibm.com>

* Make DiGraph sum deterministic

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@ibm.com>

* Remove ordered hashes/sets from DiGraphTests

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@ibm.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/src/test/scala/firrtlTests/graph/DiGraphTests.scala b/src/test/scala/firrtlTests/graph/DiGraphTests.scala
index b9f51699..147b22d7 100644
--- a/src/test/scala/firrtlTests/graph/DiGraphTests.scala
+++ b/src/test/scala/firrtlTests/graph/DiGraphTests.scala
@@ -58,4 +58,18 @@ class DiGraphTests extends FirrtlFlatSpec {
     tupleGraph.transformNodes(_._1).getEdgeMap should contain ("a" -> Set("b", "c"))
   }
 
+  "Graph summation" should "be order-wise equivalent to original" in {
+    val first = acyclicGraph.subgraph(Set("a", "b", "c"))
+    val second = acyclicGraph.subgraph(Set("b", "c", "d", "e"))
+
+    (first + second).getEdgeMap should equal (acyclicGraph.getEdgeMap)
+  }
+
+  it should "be idempotent" in {
+    val first = acyclicGraph.subgraph(Set("a", "b", "c"))
+    val second = acyclicGraph.subgraph(Set("b", "c", "d", "e"))
+
+    (first + second + second + second).getEdgeMap should equal (acyclicGraph.getEdgeMap)
+  }
+
 }