Make the 'is' routine in Test not throwing an error on failure when t…

…he type can't be stringified, falling back on .raku instead.

A good example is the Buf type that has a Str routine that fail to encourage the user to use encode instead.

is Buf.new(42), Buf.new(43)

This will fail with the error :
Cannot use a Buf as a string, but you called the Stringy method on it
instead of the regular got, expected message.

This fix issue #3535

lib/Test.rakumod

@@ -188,8 +188,15 @@ multi sub is(Mu $got, Mu:D $expected, $desc = '') is export {
                     ~ "     got: $got.raku()";
             }
             else {
-                _diag "expected: '$expected'\n"
+		try { # if the type support Stringification
+                      # note: we can't use ^can('Str') as Buf error in its Str method itself
+                    _diag "expected: '$expected'\n"
                     ~ "     got: '$got'";
+                    True;
+                } or {
+                    _diag "expected: $expected.raku()\n"
+                    ~ "     got: $got.raku()";
+                }
             }
         }
     }

t/01-sanity/99-test-basic.t

@@ -142,6 +142,14 @@ todo( 'failing is-deeply returns False' );
 my $is-deeply = is-deeply {a => 1}, {}, 'is-deeply with exta key fails';
 nok $is-deeply, 'failing is-deeply returns False';
 
+# Testing issue #3535
+is Buf.new(42), Buf.new(42), "Comparing eq Buf";
+lives-ok {
+    # NOT_TODO
+    todo("Comparing 2 not eq Buf, should not pass");
+    is Buf.new(42), Buf.new(43);
+}, "Comparing neq Buf";
+
 done-testing;
 
 # vim: ft=perl6