1 files changed, 46 insertions, 0 deletions
diff --git a/src/internal/dag/alg_test.go b/src/internal/dag/alg_test.go
new file mode 100644
index 0000000000..e5ea8b6ab6
--- /dev/null
+++ b/src/internal/dag/alg_test.go
@@ -0,0 +1,46 @@
+// Copyright 2022 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package dag
+
+import (
+	"reflect"
+	"strings"
+	"testing"
+)
+
+func TestTranspose(t *testing.T) {
+	g := mustParse(t, diamond)
+	g.Transpose()
+	wantEdges(t, g, "a->b a->c a->d b->d c->d")
+}
+
+func TestTopo(t *testing.T) {
+	g := mustParse(t, diamond)
+	got := g.Topo()
+	// "d" is the root, so it's first.
+	//
+	// "c" and "b" could be in either order, but Topo is
+	// deterministic in reverse node definition order.
+	//
+	// "a" is a leaf.
+	wantNodes := strings.Fields("d c b a")
+	if !reflect.DeepEqual(wantNodes, got) {
+		t.Fatalf("want topo sort %v, got %v", wantNodes, got)
+	}
+}
+
+func TestTransitiveReduction(t *testing.T) {
+	t.Run("diamond", func(t *testing.T) {
+		g := mustParse(t, diamond)
+		g.TransitiveReduction()
+		wantEdges(t, g, "b->a c->a d->b d->c")
+	})
+	t.Run("chain", func(t *testing.T) {
+		const chain = `NONE < a < b < c < d; a, d < e;`
+		g := mustParse(t, chain)
+		g.TransitiveReduction()
+		wantEdges(t, g, "e->d d->c c->b b->a")
+	})
+}