diff --git a/tests/tests/test_bip85.py b/tests/tests/test_bip85.py
index e5ec9c4..a75fee3 100644
--- a/tests/tests/test_bip85.py
+++ b/tests/tests/test_bip85.py
@@ -48,12 +48,44 @@
 
 
 class Bip85Test(TestCase):
+
+    def test_derive_entropy(self):
+        for app_index, path, expected in [
+            (39, [0, 12, 0], unhexlify("6250b68daf746d12a24d58b4787a714bf1b58d69e4c2a466276fb16fe93dc52b6fac6b756894072241447cad56f6405ee326dbb473d2f5e943543590082927c0")),
+            (2, [0], unhexlify("7040bb53104f27367f317558e78a994ada7296c6fde36a364e5baf206e502bb1f988080b7dd814e7ae7d6d83edbb6689886a560e165f4a740877cdf3beecacf8")),
+            (32, [0], unhexlify("52405cd0dd21c5be78314a7c1a3c65ffd8d896536cc7dee3157db5824f0c92e2ead0b33988a616cf6a497f1c169d9e92562604e38305ccd3fc96f2252c177682")),
+        ]:
+            result = bip85.derive_entropy(ROOT, app_index, path)
+            self.assertEqual(result, expected)
+
+    def test_derive_entropy_fail_path_ge_hardened_index(self):
+        with self.assertRaises(ValueError) as exc:
+            bip85.derive_entropy(ROOT, 39, [bip32.HARDENED_INDEX + 1])
+        self.assertEqual(str(exc.exception), "Path elements must be less than 2^31")
+
     def test_bip39(self):
         for num_words, index, lang, expected in VECTORS_BIP39:
             self.assertEqual(
                 bip85.derive_mnemonic(ROOT, num_words, index, language=lang), expected
             )
 
+    def test_bip39_fail_num_words(self):
+        cases = [
+            (11, 0, bip85.LANGUAGES.ENGLISH),
+            (13, 0, bip85.LANGUAGES.ENGLISH),
+            (15, 0, bip85.LANGUAGES.ENGLISH),
+            (17, 0, bip85.LANGUAGES.ENGLISH),
+            (19, 0, bip85.LANGUAGES.ENGLISH),
+            (21, 0, bip85.LANGUAGES.ENGLISH),
+            (23, 0, bip85.LANGUAGES.ENGLISH),
+            (25, 0, bip85.LANGUAGES.ENGLISH),
+        ]
+
+        for num_words, index, lang in cases:
+            with self.assertRaises(ValueError) as exc:
+                bip85.derive_mnemonic(ROOT, num_words, index, language=lang)
+            self.assertEqual(str(exc.exception), "Number of words must be 12, 18 or 24")
+
     def test_wif(self):
         for idx, expected in VECTORS_WIF:
             self.assertEqual(bip85.derive_wif(ROOT, idx).wif(), expected)
@@ -67,3 +99,15 @@ def test_hex(self):
             self.assertEqual(
                 bip85.derive_hex(ROOT, num_bytes, idx), unhexlify(expected)
             )
+
+    def test_hex_fail_num_bytes_ge_64(self):
+        for num_bytes in [65, 100, 1000, 10000]:
+            with self.assertRaises(ValueError) as exc:
+                bip85.derive_hex(ROOT, num_bytes, 1)
+            self.assertEqual(str(exc.exception), "Number of bytes must be less than 64")
+
+    def test_hex_fail_num_bytes_le_16(self):
+        for num_bytes in [15, 14, 10, 0]:
+            with self.assertRaises(ValueError) as exc:
+                bip85.derive_hex(ROOT, num_bytes, 2)
+            self.assertEqual(str(exc.exception), "Number of bytes must be at least 16")