Add experimental support for testing metrics

lib/Test2/Tools/OpenTelemetry.pm

@@ -4,11 +4,20 @@ package
 our $VERSION = '0.001';
 
 use Exporter 'import';
-our @EXPORT = qw( messages no_messages );
+our @EXPORT = qw(
+    messages
+    no_messages
+    metrics
+    no_metrics
+);
 
+use Feature::Compat::Defer;
 use Test2::API 'context';
 use Test2::Compare qw( compare strict_convert );
 
+# TODO: Cannot lexically set a metrics adapter
+use Metrics::Any::Adapter 'Test';
+
 require Log::Any::Adapter;
 
 my $capture_messages = sub {
@@ -44,4 +53,35 @@ sub no_messages (&) {
     return !$delta;
 }
 
+my $capture_metrics = sub {
+    my $code = shift;
+
+    Metrics::Any::Adapter::Test->clear;
+    defer { Metrics::Any::Adapter::Test->clear }
+
+    $code->();
+
+    [ split /\n/, Metrics::Any::Adapter::Test->metrics ];
+};
+
+sub metrics (&) { goto $capture_metrics }
+
+sub no_metrics (&) {
+    my $name = 'No metrics collected';
+
+    my $data    = shift->$capture_metrics;
+    my $context = context;
+    my $delta   = compare $data, [], \&strict_convert;
+
+    if ( $delta ) {
+        $context->fail( $name, $delta->diag );
+    }
+    else {
+        $context->ok( 1, $name );
+    }
+
+    $context->release;
+    return !$delta;
+}
+
 1;