Fix some bounds in rapid check instances

`inRange` is exclusive not inclusive:
https://github.com/emil-e/rapidcheck/blob/master/doc/generators.md#usage

Furthermore, use `std::variant_size_v` so we use the right number
automatically.

Finally, make the `switch` assert the discriminant is in bounds as
expected.

1 files changed, 4 insertions, 2 deletions

diff --git a/src/libstore/tests/derived-path.cc b/src/libstore/tests/derived-path.cc
index e6d32dbd0..160443ec1 100644
--- a/src/libstore/tests/derived-path.cc
+++ b/src/libstore/tests/derived-path.cc
@@ -27,11 +27,13 @@ Gen<DerivedPath::Built> Arbitrary<DerivedPath::Built>::arbitrary()
 
 Gen<DerivedPath> Arbitrary<DerivedPath>::arbitrary()
 {
-    switch (*gen::inRange<uint8_t>(0, 1)) {
+    switch (*gen::inRange<uint8_t>(0, std::variant_size_v<DerivedPath::Raw>)) {
     case 0:
         return gen::just<DerivedPath>(*gen::arbitrary<DerivedPath::Opaque>());
-    default:
+    case 1:
         return gen::just<DerivedPath>(*gen::arbitrary<DerivedPath::Built>());
+    default:
+        assert(false);
     }
 }