fixup! Add test for splitX bug fix covering logic handling splits on edges

    kirr@deco:~/src/neo/src/github.com/cznic/b$ go test ./...
    # github.com/cznic/b
    ./all_test.go:483:3: Fatalf format %v reads arg #3, but call has 2 args
    ./all_test.go:518:3: Fatalf format %v reads arg #3, but call has 2 args

all_test.go

@@ -480,7 +480,7 @@ func TestSplitXOnEdge(t *testing.T) {
 	// if splitX was wrong kedge:777 would land into wrong place with Get failing
 	v, ok := tr.Get(kedge)
 	if !(v==777 && ok) {
-		t.Fatalf("after splitX: Get(%v) -> %v, %v  ; expected 777, true", v, ok)
+		t.Fatalf("after splitX: Get(%v) -> %v, %v  ; expected 777, true", kedge, v, ok)
 	}
 
 	// now check the same when splitted X has parent
@@ -515,7 +515,7 @@ func TestSplitXOnEdge(t *testing.T) {
 	// if splitX was wrong kedge:888 would land into wrong place
 	v, ok = tr.Get(kedge)
 	if !(v==888 && ok) {
-		t.Fatalf("after splitX: Get(%v) -> %v, %v  ; expected 888, true", v, ok)
+		t.Fatalf("after splitX: Get(%v) -> %v, %v  ; expected 888, true", kedge, v, ok)
 	}
 }