Spec custom parametarization of Rational

S32-num/rat.t

@@ -3,7 +3,7 @@ use lib <t/spec/packages>;
 use Test;
 use Test::Util;
 
-plan 845;
+plan 846;
 
 # Basic test functions specific to rational numbers.
 
@@ -444,4 +444,31 @@ subtest '.^roles on Rationals does not hang' => {
         'custom class :D';
 }
 
+subtest 'custom parametarization of Rational' => {
+    # Prametartion with no args defaults to `Int` for both args
+    # If only one arg is given, the type of the second arg is the same as the first
+    plan 12;
+
+    my class FakeRat   does Rational             {}
+    my class FakeRatU  does Rational[UInt      ] {}
+    my class FakeRatUU does Rational[UInt, UInt] {}
+    my class FakeRatIU does Rational[Int,  UInt] {}
+    my class FakeRatII does Rational[Int,   Int] {}
+
+    isa-ok FakeRat  .new(-1,  1), FakeRat,   'no parametarization; 2 Ints';
+    isa-ok FakeRatU .new( 1,  1), FakeRatU,  '[UInt];       2 UInts';
+    isa-ok FakeRatUU.new( 1,  1), FakeRatUU, '[UInt, UInt]; 2 UInts';
+    isa-ok FakeRatIU.new(-1,  1), FakeRatIU, '[Int,  UInt]; Int, UInt';
+    isa-ok FakeRatII.new(-1, -1), FakeRatII, '[Int,  Int]; 2 Ints';
+
+    constant E = X::TypeCheck;
+    throws-like { FakeRat  .new: 1e0, 1   }, E, 'no parametarization; Num, Int';
+    throws-like { FakeRat  .new: 1e0, 1e0 }, E, 'no parametarization; 2 Nums';
+    throws-like { FakeRat  .new:   1, 1e0 }, E, 'no parametarization; Int, Num';
+    throws-like { FakeRatU .new:  -1,   1 }, E, '[UInt]; Int, UInt';
+    throws-like { FakeRatUU.new:   1,  -1 }, E, '[UInt, UInt]; UInt, Int';
+    throws-like { FakeRatIU.new:   1,  -1 }, E, '[Int,  UInt]; UInt, Int';
+    throws-like { FakeRatII.new: 1e0, 1e0 }, E, '[Int,  Int]; 2 Nums';
+}
+
 # vim: ft=perl6