chess: add more benchmark cases for generating legal moves

internal/chess/movegen_test.go

@@ -1,15 +1,43 @@
 package chess
 
-import "testing"
-
-func BenchmarkGenerateLegalMoves(b *testing.B) {
-	position, _ := NewPosition(StartingFen)
+import (
+	"fmt"
+	"testing"
+)
 
+func generateLegalMovesBenchmark(b *testing.B, fen string) {
+	position, _ := NewPosition(fen)
 	for i := 0; i < b.N; i++ {
 		position.GenerateMoves(LegalMoveGeneration)
 	}
 }
 
+func BenchmarkGenerateLegalMoves(b *testing.B) {
+	cases := []struct {
+		Name string
+		Fen  string
+	}{
+		{
+			Name: "StartingPosition",
+			Fen:  StartingFen,
+		},
+		{
+			Name: "LargestNumberOfLegalMoves",
+			Fen:  "R6R/3Q4/1Q4Q1/4Q3/2Q4Q/Q4Q2/pp1Q4/kBNNK1B1 w - - 0 1",
+		},
+		{
+			Name: "InCheck",
+			Fen:  "rn2kbnr/ppp2ppp/3pb3/4p3/2B1q3/BPN5/P1PP1PPP/R2QK1NR w KQkq - 0 6",
+		},
+	}
+
+	for _, c := range cases {
+		b.Run(fmt.Sprintf("%s", c.Name), func(b *testing.B) {
+			generateLegalMovesBenchmark(b, c.Fen)
+		})
+	}
+}
+
 func BenchmarkGenerateCaptureMoves(b *testing.B) {
 	position, _ := NewPosition(StartingFen)