t/class/accessor.t - add additional :reader and :writer tests

The :reader tests are not really needed at present, as `pp_leavesub` makes
the necessary copies, but exploring some fast accessor ideas which bypass
that logic has shown the usefulness of having these tests present.

The :writer tests verify that user errors are handled as expected.

Author: richardleach

t/class/accessor.t

@@ -19,7 +19,10 @@ no warnings 'experimental::class';
         field @a :reader = qw( the array );
 
         # Present-but-empty parens counts as default
+
         field %h :reader() = qw( the hash );
+
+        field $empty :reader;
     }
 
     my $o = Testcase1->new;
@@ -35,12 +38,26 @@ no warnings 'experimental::class';
         'Reader accessor fails with argument');
     like($@, qr/^Too many arguments for subroutine \'Testcase1::s\' \(got 2; expected 1\) at /,
         'Failure from argument to accessor');
+
+    # Reading an undefined value has predictable behaviour
+    $o->empty;
+    pass("void :reader on an uninitialized field doesn't crash");
+    ok(!defined scalar $o->empty, 'scalar :reader on uninitialized field is undef');
+    my ($empty) = $o->empty;
+    ok(!defined $empty, 'list :reader on uninitialized field is undef');
+
+    # :reader returns value copies, not the internal SVs
+    map { $_ = 99 } $o->s, $o->a, $o->h;
+    is($o->s, "the scalar", ':reader does not expose internal SVs');
+    ok(eq_array([$o->a], [qw( the array )]), ':reader does not expose internal AVs');
+    ok(eq_hash({$o->h}, {qw( the hash )}), ':reader does not expose internal HVs');
 }
 
 # writer accessors on scalars
 {
     class Testcase2 {
         field $s :reader :writer = "initial";
+        field $xno :param :reader = "Eh-ehhh";
     }
 
     my $o = Testcase2->new;
@@ -57,6 +74,12 @@ no warnings 'experimental::class';
         'Writer accessor fails with 2 arguments');
     like($@, qr/^Too many arguments for subroutine \'Testcase2::set_s\' \(got 3; expected 2\) at /,
         'Failure from argument to accessor');
+
+    # Should not be able to write without the :writer attribute
+    ok(!eval { $o->set_xno(77) },
+        'Cannot write without :writer attribute');
+    like($@, qr/^Can\'t locate object method \"set_xno\" via package \"Testcase2\"/,
+        'Failure from writing without :writer');
 }
 
 # Alternative names
@@ -76,4 +99,16 @@ no warnings 'experimental::class';
        'Failure from lack of original name accessor');
 }
 
+# writer accessors on AVs or HVs
+{
+    ok(!eval "class Testcase4 { field \@a :writer; }",
+        'Cannot assign a :writer to an array field');
+    like($@, qr/^Cannot apply a :writer attribute to a non-scalar field/,
+        'Failure from assigning :writer to an array field');
+    ok(!eval "class Testcase5 { field \%h :writer; }",
+        'Cannot assign a :writer to an hash field');
+    like($@, qr/^Cannot apply a :writer attribute to a non-scalar field/,
+        'Failure from assigning :writer to an hash field');
+}
+
 done_testing;