diff --git a/core/tests/test_apps.wallet.sign_tx.writers.py b/core/tests/test_apps.wallet.sign_tx.writers.py
new file mode 100644
index 000000000..7f8a2a985
--- /dev/null
+++ b/core/tests/test_apps.wallet.sign_tx.writers.py
@@ -0,0 +1,54 @@
+from common import *
+
+from trezor.messages.TxInputType import TxInputType
+from trezor.messages import InputScriptType
+
+from apps.common import coins
+from apps.common.seed import Keychain
+from apps.wallet.sign_tx import writers
+
+
+class TestWriters(unittest.TestCase):
+    def test_tx_input(self):
+        inp = TxInputType(
+            address_n=[0],
+            amount=390000,
+            prev_hash=unhexlify(
+                "d5f65ee80147b4bcc70b75e4bbf2d7382021b871bd8867ef8fa525ef50864882"
+            ),
+            prev_index=0,
+            sequence=0xffffffff,
+            script_sig=b"0123456789",
+        )
+
+        b = bytearray()
+        writers.write_tx_input(b, inp)
+        self.assertEqual(len(b), 32 + 4 + 1 + 10 + 4)
+
+        for bad_prevhash in (b"", b"x", b"hello", b"x" * 33):
+            inp.prev_hash = bad_prevhash
+            self.assertRaises(AssertionError, writers.write_tx_input, b, inp)
+
+    def test_tx_input_check(self):
+        inp = TxInputType(
+            address_n=[0],
+            amount=390000,
+            prev_hash=unhexlify(
+                "d5f65ee80147b4bcc70b75e4bbf2d7382021b871bd8867ef8fa525ef50864882"
+            ),
+            prev_index=0,
+            script_type=InputScriptType.SPENDWITNESS,
+            sequence=0xffffffff,
+            script_sig=b"0123456789",
+        )
+
+        b = bytearray()
+        writers.write_tx_input_check(b, inp)
+        self.assertEqual(len(b), 32 + 4 + 4 + 4 + 4 + 4 + 8)
+
+        for bad_prevhash in (b"", b"x", b"hello", b"x" * 33):
+            inp.prev_hash = bad_prevhash
+            self.assertRaises(AssertionError, writers.write_tx_input_check, b, inp)
+
+if __name__ == "__main__":
+    unittest.main()