Add basic "use trace" sanity test

t/01-sanity/55-use-trace.t

@@ -0,0 +1,35 @@
+use v6;
+
+use Test;
+
+plan 3;
+
+my $filename = "$?FILE.trace";
+my $stderr   = "$filename.stderr";
+
+spurt( $filename, q:to/CODE/ );
+my $a = 42;
+if $a {
+    use trace;
+    $a++;
+    no trace;
+    $a--;
+}
+$a += 1;
+use trace;
+$a -= 1;
+no trace;
+say $a;
+CODE
+
+my $p = pipe( "$*EXECUTABLE $filename 2>$stderr" );
+ok $p,                            "did we get a handle?";
+is $p.lines.join, "42",           "is the program output ok?";
+is slurp($stderr), qq:to/STDERR/, "is the trace ok?";
+4 ($filename:4)
+\$a++
+10 ($filename:10)
+\$a -= 1
+STDERR
+
+unlink $filename, $stderr;