Rename from Box to AsBox and add unit tests

The new name has better consistency with other existing conversion
functions (e.g. `AsGeometry` and `AsPolygon`).

CHANGELOG.md

@@ -12,8 +12,8 @@
 
 - R-tree improvements that reduce the amount of memory they use.
 
-- Exposes a `Box() rtree.Box` method on the `geom.Envelope` type, that converts
-  the envelope to an `rtree.Box`.
+- Exposes an `AsBox() rtree.Box` method on the `geom.Envelope` type, that
+  converts the envelope to an `rtree.Box`.
 
 ## v0.43.0
 

geom/type_envelope.go

@@ -287,8 +287,8 @@ func (e Envelope) TransformXY(fn func(XY) XY) (Envelope, error) {
 	return NewEnvelope([]XY{fn(min), fn(max)})
 }
 
-// Box converts this Envelope to an rtree.Box.
-func (e Envelope) Box() (rtree.Box, bool) {
+// AsBox converts this Envelope to an rtree.Box.
+func (e Envelope) AsBox() (rtree.Box, bool) {
 	return rtree.Box{
 		MinX: e.minX(),
 		MinY: e.minY,

geom/type_envelope_test.go

@@ -7,6 +7,7 @@ import (
 	"testing"
 
 	. "github.com/peterstace/simplefeatures/geom"
+	"github.com/peterstace/simplefeatures/rtree"
 )
 
 func onePtEnv(x, y float64) Envelope {
@@ -609,3 +610,15 @@ func TestBoundingDiagonal(t *testing.T) {
 		})
 	}
 }
+
+func TestEnvelopeEmptyAsBox(t *testing.T) {
+	_, ok := Envelope{}.AsBox()
+	expectFalse(t, ok)
+}
+
+func TestEnvelopeNonEmptyAsBox(t *testing.T) {
+	got, ok := twoPtEnv(1, 2, 3, 4).AsBox()
+	expectTrue(t, ok)
+	want := rtree.Box{MinX: 1, MinY: 2, MaxX: 3, MaxY: 4}
+	expectTrue(t, got == want)
+}

geom/type_multi_polygon.go

@@ -65,7 +65,7 @@ func validateMultiPolygon(polys []Polygon, opts ctorOptionSet) error {
 	boxes := make([]rtree.Box, len(polys))
 	items := make([]rtree.BulkItem, 0, len(polys))
 	for i, p := range polys {
-		if box, ok := p.Envelope().Box(); ok {
+		if box, ok := p.Envelope().AsBox(); ok {
 			boxes[i] = box
 			item := rtree.BulkItem{Box: boxes[i], RecordID: i}
 			items = append(items, item)

geom/type_polygon.go

@@ -80,7 +80,7 @@ func validatePolygon(rings []LineString, opts ctorOptionSet) error {
 	boxes := make([]rtree.Box, len(rings))
 	items := make([]rtree.BulkItem, len(rings))
 	for i, r := range rings {
-		box, ok := r.Envelope().Box()
+		box, ok := r.Envelope().AsBox()
 		if !ok {
 			// Cannot occur, because we have already checked to ensure rings
 			// are closed. Closed rings by definition are non-empty.