Add test checks that tries meet the invariant condition.

trie/add_test.go

@@ -16,6 +16,8 @@ func TestMutableAndImmutableAddSame(t *testing.T) {
 			mut.Add(k)
 			immut = Add(immut, k)
 		}
+		mut.CheckInvariant()
+		immut.CheckInvariant()
 		if !Equal(mut, immut) {
 			t.Errorf("mutable trie %v differs from immutable trie %v", mut, immut)
 		}
@@ -28,12 +30,14 @@ func TestAddIsOrderIndependent(t *testing.T) {
 		for _, k := range s.Keys {
 			base.Add(k)
 		}
+		base.CheckInvariant()
 		for j := 0; j < 100; j++ {
 			perm := rand.Perm(len(s.Keys))
 			reordered := New()
 			for i := range s.Keys {
 				reordered.Add(s.Keys[perm[i]])
 			}
+			reordered.CheckInvariant()
 			if !Equal(base, reordered) {
 				t.Errorf("trie %v differs from trie %v", base, reordered)
 			}

trie/check.go

+package trie
+
+// CheckInvariant panics of the trie does not meet its invariant.
+func (trie *Trie) CheckInvariant() {
+	switch {
+	case trie.IsLeaf():
+		return
+	default:
+		if trie.IsEmpty() {
+			b0, b1 := trie.Branch[0], trie.Branch[1]
+			b0.CheckInvariant()
+			b1.CheckInvariant()
+			switch {
+			case b0.IsEmptyLeaf() && b1.IsEmptyLeaf():
+				panic("intermediate node with two empty leaves")
+			case b0.IsEmptyLeaf() && b1.IsNonEmptyLeaf():
+				panic("intermediate node with one empty leaf")
+			case b0.IsNonEmptyLeaf() && b1.IsEmptyLeaf():
+				panic("intermediate node with one empty leaf")
+			}
+		} else {
+			panic("intermediate node with a key")
+		}
+	}
+}

trie/intersect_test.go

@@ -32,13 +32,16 @@ func testIntersect(t *testing.T, sample *testIntersectSample) {
 	for _, l := range sample.LeftKeys {
 		left.Add(l)
 	}
+	left.CheckInvariant()
 	for _, r := range sample.RightKeys {
 		right.Add(r)
 	}
+	right.CheckInvariant()
 	for _, s := range setIntersect(sample.LeftKeys, sample.RightKeys) {
 		expected.Add(s)
 	}
 	got := Intersect(left, right)
+	got.CheckInvariant()
 	if !Equal(expected, got) {
 		t.Errorf("intersection of %v and %v: expected %v, got %v",
 			sample.LeftKeys, sample.RightKeys, expected, got)
@@ -113,6 +116,27 @@ var testIntersectJSONSamples = []string{
         "gAlMTjoCy6ZDZFN/0okF65fxscCLVxnQhlJsyfp6uWU=",
         "qAISv6yZjs3WWlDC89iJUSdq45F0D/1y9fLnsPvavdA="
     ]
+}
+	`,
+	`
+{
+    "LeftKeys": [
+        "BXmU8txOqn8ExHzXuXRtHm2XM99uD8lsgPo8OdDcNYE=",
+        "hVzcamVYfIqs4IlrVIM1qRalqTh8OMrlAeqwgJTI2xo=",
+        "JbILHEM3RcA+ksq0BvU+9Zfc+jnpsxPUQLe9lrHqBwc=",
+        "VUeFiK5V64F8G2rvnIyoopfOzICF0h79FmeiLQqrVAI=",
+        "tYRdsKlUTbTXOpgVjUZtzh2DRG0e5nPXIrkN60PI5GE=",
+        "LatyclJiSPEaCoLxbabddv7Rqrsy+J1hf2Pd9BmmN1U=",
+        "XX0wXrGF4IytkKmStxesXOiGFK+dm5ran6lWu7xNhIw=",
+        "PcZb8TBEHhEqpFfaRWyhit3Uc03895uOkMgiiBgW9Uk="
+    ],
+    "RightKeys": [
+        "BXmU8txOqn8ExHzXuXRtHm2XM99uD8lsgPo8OdDcNYE=",
+        "hVzcamVYfIqs4IlrVIM1qRalqTh8OMrlAeqwgJTI2xo=",
+        "VUeFiK5V64F8G2rvnIyoopfOzICF0h79FmeiLQqrVAI=",
+        "tYRdsKlUTbTXOpgVjUZtzh2DRG0e5nPXIrkN60PI5GE=",
+        "XX0wXrGF4IytkKmStxesXOiGFK+dm5ran6lWu7xNhIw="
+    ]
 }
 	`,
 }