Add examples to simplify tests requiring keys

tests/examples.nim

@@ -0,0 +1,7 @@
+import abc/keys
+
+proc example*(_: type PrivateKey): PrivateKey =
+  PrivateKey.random
+
+proc example*(_: type PublicKey): PublicKey =
+  PrivateKey.example.toPublicKey

tests/testKeys.nim

@@ -2,6 +2,7 @@ import std/unittest
 import pkg/questionable
 import pkg/stew/byteutils
 import abc/keys
+import ./examples
 
 suite "Keys":
 
@@ -9,40 +10,40 @@ suite "Keys":
     check PrivateKey.random != PrivateKey.random
 
   test "erases memory associated with a private key":
-    var key = PrivateKey.random
+    var key = PrivateKey.example
     let bytes = cast[ptr[uint64]](addr key)
     check bytes[] != 0
     erase key
     check bytes[] == 0
 
   test "derives public key from private key":
-    let key1, key2 = PrivateKey.random()
+    let key1, key2 = PrivateKey.example
     check key1.toPublicKey == key1.toPublicKey
     check key2.toPublicKey == key2.toPublicKey
     check key1.toPublicKey != key2.toPublicKey
 
   test "can be used to sign messages":
     const message = "hello".toBytes
-    let key = PrivateKey.random()
+    let key = PrivateKey.example
     let signature = key.sign(message)
     check signature != Signature.default
 
   test "can be used to verify signatures":
     let message1 = "hello".toBytes
     let message2 = "hallo".toBytes
-    let private = PrivateKey.random
+    let private = PrivateKey.example
     let public = private.toPublicKey
     let signature = private.sign(message1)
     check public.verify(message1, signature)
     check not public.verify(message2, signature)
 
   test "public key can be converted to bytes":
-    let key = PrivateKey.random.toPublicKey
+    let key = PublicKey.example
     let bytes = key.toBytes
     check PublicKey.fromBytes(bytes) == key.some
 
   test "conversion from bytes to public key can fail":
-    let key = PrivateKey.random.toPublicKey
+    let key = PublicKey.example
     let bytes = key.toBytes
     let invalid = bytes[1..^1]
     check PublicKey.fromBytes(invalid) == PublicKey.none