test(core): add unit tests for PaymentRequestVerifier

diff --git a/core/tests/test_apps.common.payment_request.py b/core/tests/test_apps.common.payment_request.py
new file mode 100644
index 000000000..5a096ceb0
--- /dev/null
+++ b/core/tests/test_apps.common.payment_request.py
@@ -0,0 +1,240 @@
+# flake8: noqa: F403,F405
+from common import *  # isort:skip
+
+from typing import TYPE_CHECKING
+
+from mock import patch
+from trezor import wire
+from trezor.crypto import bip39
+from trezor.messages import (
+    CoinPurchaseMemo,
+    PaymentRequest,
+    PaymentRequestMemo,
+    RefundMemo,
+    TextMemo,
+)
+
+from apps.common import coins
+from apps.common.keychain import Keychain
+from apps.common.paths import AlwaysMatchingSchema
+from apps.common.payment_request import PaymentRequestVerifier
+
+if TYPE_CHECKING:
+    from typing import Callable, ParamSpec
+
+    P = ParamSpec("P")
+
+
+# Decorator that replaces DEBUG version of `verify_payment_request_is_supported` and PUBLIC_KEY
+# by the PROD versions
+def patch_prod(func: Callable[P, None]) -> Callable[P, None]:
+
+    def wrapper(*args: P.args, **kwargs: P.kwargs) -> bytes:
+        with patch(
+            PaymentRequestVerifier,
+            "_use_debug_key",
+            lambda self: None,
+        ):
+            with patch(
+                PaymentRequestVerifier,
+                "_use_debug_verification",
+                lambda self: None,
+            ):
+                return func(*args, **kwargs)
+
+    return wrapper
+
+
+# Get keychain for SLIP-24
+def _get_test_keychain() -> Keychain:
+    coin = coins.by_name("Bitcoin")
+    seed = bip39.seed(" ".join(["all"] * 12), "")
+    keychain = Keychain(
+        seed,
+        coin.curve_name,
+        [AlwaysMatchingSchema],
+        slip21_namespaces=[[b"SLIP-0024"]],
+    )
+    return keychain
+
+
+# Payment request helpers
+def _get_request_without_memos() -> PaymentRequest:
+    debug_signature = (
+        "208cd919f3c6544f390b402394570fd6d1279962c13d0cb1b8180dfe0bc614ee1"
+        "e55efcc85de5ab52a57a8ecf675d8454d6204c98298f93faf71c668fec9340070"
+    )
+    return PaymentRequest(
+        recipient_name="TEST Recipient", signature=unhexlify(debug_signature), memos=[]
+    )
+
+
+def _get_request_with_text_memo() -> PaymentRequest:
+    text_memo = TextMemo(text="text memo text")
+
+    return PaymentRequest(
+        recipient_name="TEST Recipient",
+        signature=b"\x01",
+        memos=[PaymentRequestMemo(text_memo=text_memo)],
+    )
+
+
+def _get_request_with_coin_purchase_memo() -> PaymentRequest:
+    coin_purchase_memo = CoinPurchaseMemo(
+        coin_type=0, amount="AMOUNT", address="ADDRESS", mac=b"\xde\xad\xbe\xef"
+    )
+    return PaymentRequest(
+        recipient_name="TEST Recipient",
+        signature=b"\x01",
+        memos=[PaymentRequestMemo(coin_purchase_memo=coin_purchase_memo)],
+    )
+
+
+def _get_sell_payment_request() -> PaymentRequest:
+    text_memo = TextMemo(text="text memo text")
+    mac = "a7594205d318491c7335d460acfebadc3c862b803abfd5a0fcf7ea6082bff1dc"
+    refund_memo = RefundMemo(address="ADDRESS", mac=unhexlify(mac))
+    debug_signature = (
+        "20b638bff2341f526ee99faa7afb28f72c54c535db69b25451ce7471dd8866fd1"
+        "8644a89effcc7dfb07a281bd5c516045180341c813536563ff50725f4221df5f8"
+    )
+    return PaymentRequest(
+        recipient_name="TEST Recipient",
+        signature=unhexlify(debug_signature),
+        memos=[
+            PaymentRequestMemo(text_memo=text_memo),
+            PaymentRequestMemo(refund_memo=refund_memo),
+        ],
+    )
+
+
+def _get_coin_swap_request() -> PaymentRequest:
+    mac = "08f2e807b9932596dd15831958cb1172ae5bb3c8bc8c6476b089bc045ca4d8b8"
+    mac2 = "1394db3333b67a73b9abb6f5c9afe37c2a5f8fb92aa17baf9c696ec85d2523c1"
+    debug_signature = (
+        "20a5500e61eafdfbb83643f5b2c139757f760e32a7416b92a1b07a4f1a6c307a4"
+        "149fbda45fdb98e051f3b839e63eb67bb167f32a85f8c6864a60785e304b703b1"
+    )
+    coin_purchase_memo = CoinPurchaseMemo(
+        coin_type=0, amount="AMOUNT", address="ADDRESS", mac=unhexlify(mac)
+    )
+    refund_memo = RefundMemo(address="Refund address", mac=unhexlify(mac2))
+    return PaymentRequest(
+        recipient_name="TEST Recipient",
+        signature=unhexlify(debug_signature),
+        memos=[
+            PaymentRequestMemo(coin_purchase_memo=coin_purchase_memo),
+            PaymentRequestMemo(refund_memo=refund_memo),
+        ],
+    )
+
+
+class TestPaymentRequestVerfier(unittest.TestCase):
+
+    @patch_prod
+    def test_payment_requests_unsupported_in_prod_without_memos(self):
+
+        # Unsupported - without memos
+        with self.assertRaises(wire.DataError) as e:
+            PaymentRequestVerifier(
+                payment_request=_get_request_without_memos(),
+                slip44_id=1,
+                keychain=_get_test_keychain(),
+                amount_size_bytes=12345,
+            )
+        self.assertEqual(
+            e.value.message, "Payment request must contain at least one memo."
+        )
+
+    @patch_prod
+    def test_payment_requests_unsupported_in_prod_sell(self):
+        with self.assertRaises(wire.DataError) as e:
+            PaymentRequestVerifier(
+                payment_request=_get_sell_payment_request(),
+                slip44_id=1,
+                keychain=_get_test_keychain(),
+                amount_size_bytes=12345,
+            )
+        self.assertEqual(
+            e.value.message, "Only COIN SWAP payment requests are supported."
+        )
+
+    @patch_prod
+    def test_payment_requests_unsupported_in_prod_coin_purchase_memo_only(self):
+        with self.assertRaises(wire.DataError) as e:
+            PaymentRequestVerifier(
+                payment_request=_get_request_with_coin_purchase_memo(),
+                slip44_id=1,
+                keychain=_get_test_keychain(),
+                amount_size_bytes=12345,
+            )
+        self.assertEqual(
+            e.value.message, "Only COIN SWAP payment requests are supported."
+        )
+
+    @patch_prod
+    def test_payment_requests_unsupported_in_prod_text_memo_only(self):
+        with self.assertRaises(wire.DataError) as e:
+            PaymentRequestVerifier(
+                payment_request=_get_request_with_text_memo(),
+                slip44_id=1,
+                keychain=_get_test_keychain(),
+                amount_size_bytes=12345,
+            )
+        self.assertEqual(
+            e.value.message, "Only COIN SWAP payment requests are supported."
+        )
+
+    @patch_prod
+    def test_payment_requests_supported_in_prod_coin_swap(self):
+        verifier = PaymentRequestVerifier(
+            payment_request=_get_coin_swap_request(),
+            slip44_id=1,
+            keychain=_get_test_keychain(),
+            amount_size_bytes=12345,
+        )
+
+        # Verify signature - should fail, as PROD key should be used for verification
+        with self.assertRaises(wire.DataError) as e:
+            verifier.verify()
+        self.assertEqual(e.value.message, "Invalid signature in payment request.")
+
+    def test_payment_requests_supported_in_debug_without_memos(self):
+
+        verifier = PaymentRequestVerifier(
+            payment_request=_get_request_without_memos(),
+            slip44_id=1,
+            keychain=_get_test_keychain(),
+            amount_size_bytes=12345,
+        )
+
+        # Verify signature
+        verifier.verify()
+
+    def test_payment_requests_supported_in_debug_sell(self):
+
+        verifier = PaymentRequestVerifier(
+            payment_request=_get_sell_payment_request(),
+            slip44_id=1,
+            keychain=_get_test_keychain(),
+            amount_size_bytes=12345,
+        )
+
+        # Verify signature
+        verifier.verify()
+
+    def test_payment_requests_supported_in_debug_coin_swap(self):
+
+        verifier = PaymentRequestVerifier(
+            payment_request=_get_coin_swap_request(),
+            slip44_id=1,
+            keychain=_get_test_keychain(),
+            amount_size_bytes=12345,
+        )
+
+        # Verify signature
+        verifier.verify()
+
+
+if __name__ == "__main__":
+    unittest.main()