txscript: add tests for new P2A awareness

diff --git a/txscript/p2a_test.go b/txscript/p2a_test.go
new file mode 100644
index 0000000..bb90457
--- /dev/null
+++ b/txscript/p2a_test.go
@@ -0,0 +1,157 @@
+package txscript
+
+import (
+	"encoding/hex"
+	"testing"
+
+	"github.com/btcsuite/btcd/chaincfg"
+)
+
+// TestIsPayToAnchorScript tests the IsPayToAnchorScript function.
+func TestIsPayToAnchorScript(t *testing.T) {
+	tests := []struct {
+		name   string
+		script []byte
+		want   bool
+	}{
+		{
+			name:   "valid P2A script",
+			script: PayToAnchorScript,
+			want:   true,
+		},
+		{
+			name:   "invalid - wrong data",
+			script: []byte{OP_1, OP_DATA_2, 0x4e, 0x74},
+			want:   false,
+		},
+		{
+			name:   "invalid - wrong length",
+			script: []byte{OP_1, OP_DATA_2, 0x4e},
+			want:   false,
+		},
+		{
+			name:   "invalid - wrong version",
+			script: []byte{OP_0, OP_DATA_2, 0x4e, 0x73},
+			want:   false,
+		},
+		{
+			name: "invalid - P2WPKH",
+			script: []byte{
+				OP_0, OP_DATA_20, 0x00, 0x01, 0x02, 0x03, 0x04,
+				0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c,
+				0x0d, 0x0e, 0x0f, 0x10, 0x11, 0x12, 0x13,
+			},
+			want: false,
+		},
+		{
+			name:   "empty script",
+			script: []byte{},
+			want:   false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := IsPayToAnchorScript(tt.script)
+			if got != tt.want {
+				t.Errorf(
+					"IsPayToAnchorScript() = %v, want %v",
+					got, tt.want,
+				)
+			}
+		})
+	}
+}
+
+// TestGetScriptClassP2A tests that P2A scripts are properly classified.
+func TestGetScriptClassP2A(t *testing.T) {
+	p2aScript := PayToAnchorScript
+
+	class := GetScriptClass(p2aScript)
+	if class != PayToAnchorTy {
+		t.Errorf("GetScriptClass() = %v, want %v", class, PayToAnchorTy)
+	}
+
+	if class.String() != "anchor" {
+		t.Errorf("PayToAnchorTy.String() = %v, want 'anchor'",
+			class.String())
+	}
+
+	// Test that regular taproot scripts are still recognized as
+	// WitnessV1TaprootTy.
+	taprootScript := []byte{
+		OP_1, OP_DATA_32,
+		0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+		0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
+		0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
+		0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
+	}
+	class = GetScriptClass(taprootScript)
+	if class != WitnessV1TaprootTy {
+		t.Errorf("GetScriptClass(taproot) = %v, want %v",
+			class, WitnessV1TaprootTy)
+	}
+}
+
+// TestExtractPkScriptAddrs_P2A tests ExtractPkScriptAddrs with P2A scripts.
+func TestExtractPkScriptAddrs_P2A(t *testing.T) {
+	p2aScript := PayToAnchorScript
+
+	class, addrs, reqSigs, err := ExtractPkScriptAddrs(
+		p2aScript, &chaincfg.MainNetParams,
+	)
+	if err != nil {
+		t.Fatalf("ExtractPkScriptAddrs() error = %v", err)
+	}
+
+	if class != PayToAnchorTy {
+		t.Errorf("ExtractPkScriptAddrs() class = %v, want %v",
+			class, PayToAnchorTy)
+	}
+
+	if len(addrs) != 1 {
+		t.Fatalf("ExtractPkScriptAddrs() addrs = %v, want 1 entry",
+			addrs)
+	}
+	const wantAddr = "bc1pfeessrawgf"
+	if addrs[0].EncodeAddress() != wantAddr {
+		t.Errorf("ExtractPkScriptAddrs() addrs[0] = %v, want %v",
+			addrs[0].EncodeAddress(), wantAddr)
+	}
+
+	if reqSigs != 0 {
+		t.Errorf("ExtractPkScriptAddrs() reqSigs = %v, want 0", reqSigs)
+	}
+}
+
+// TestExpectedInputs_P2A tests that P2A scripts require no inputs.
+func TestExpectedInputs_P2A(t *testing.T) {
+	p2aScript := PayToAnchorScript
+
+	inputs := expectedInputs(p2aScript, PayToAnchorTy)
+	if inputs != 0 {
+		t.Errorf("expectedInputs() = %v, want 0", inputs)
+	}
+}
+
+// TestP2AScriptHex tests P2A script in hex format.
+func TestP2AScriptHex(t *testing.T) {
+	// The P2A script in hex should be "51024e73".
+	expectedHex := "51024e73"
+	p2aScript := PayToAnchorScript
+
+	actualHex := hex.EncodeToString(p2aScript)
+	if actualHex != expectedHex {
+		t.Errorf("P2A script hex = %v, want %v", actualHex, expectedHex)
+	}
+
+	// Test decoding.
+	decoded, err := hex.DecodeString(expectedHex)
+	if err != nil {
+		t.Fatalf("Failed to decode hex: %v", err)
+	}
+
+	if !IsPayToAnchorScript(decoded) {
+		t.Error("Decoded hex not recognized as P2A script")
+	}
+}