Extend fuzz tests

s2/encode_fuzz_test.go

@@ -1,12 +1,12 @@
-// Fuzz tests for s2 decoding. Run using
-// go test -fuzz=Fuzz github.com/golang/geo/s2
+// Fuzz tests for s2 decoding.
 package s2
 
 import (
 	"bytes"
 	"testing"
 )
 
+// go test -fuzz=FuzzDecodeCellUnion github.com/golang/geo/s2
 func FuzzDecodeCellUnion(f *testing.F) {
 	cu := CellUnion([]CellID{
 		CellID(0x33),
@@ -28,6 +28,39 @@ func FuzzDecodeCellUnion(f *testing.F) {
 		if got := c.ApproxArea(); got < 0 {
 			t.Errorf("ApproxArea() = %v, want >= 0. CellUnion: %v", got, c)
 		}
-		// TODO: Test more invariants that should hold for all CellUnion.
+		buf := new(bytes.Buffer)
+		if err := c.Encode(buf); err != nil {
+			// Re-encoding the cell union does not necessarily produce the same bytes, as there could be additional bytes following after n cells were read.
+			t.Errorf("encode() = %v. got %v, want %v. CellUnion: %v", err, buf.Bytes(), encoded, c)
+		}
+		if c.IsValid() {
+			c.Normalize()
+			if !c.IsNormalized() {
+				t.Errorf("IsNormalized() = false, want true. CellUnion: %v", c)
+			}
+		}
+	})
+}
+
+// go test -fuzz=FuzzDecodePolygon github.com/golang/geo/s2
+func FuzzDecodePolygon(f *testing.F) {
+	for _, p := range []*Polygon{near0Polygon, near01Polygon, near30Polygon, near23Polygon, far01Polygon, far21Polygon, south0abPolygon} {
+		buf := new(bytes.Buffer)
+		if err := p.Encode(buf); err != nil {
+			f.Errorf("error encoding %v: ", err)
+		}
+		f.Add(buf.Bytes())
+	}
+
+	f.Fuzz(func(t *testing.T, encoded []byte) {
+		p := &Polygon{}
+		if err := p.Decode(bytes.NewReader(encoded)); err != nil {
+			// Construction failed, no need to test further.
+			return
+		}
+		if got := p.Area(); got < 0 {
+			t.Errorf("Area() = %v, want >= 0. Polygon: %v", got, p)
+		}
+		// TODO: Test more methods on Polygon.
 	})
 }