test: add register checks for extensions

tests/ApplicationBuilderExtensionsTests.cs

@@ -0,0 +1,70 @@
+using System;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.DependencyInjection;
+using Prometheus.Client.Collectors;
+using Xunit;
+
+namespace Prometheus.Client.HttpRequestDurations.Tests;
+
+public class ApplicationBuilderExtensionsTests
+{
+    private readonly ServiceCollection _services = new();
+
+    [Fact]
+    public void AppBuilderIsNull_Throws_ArgumentNullException()
+    {
+        Assert.Throws<ArgumentNullException>(() => ((ApplicationBuilder)null).UsePrometheusRequestDurations());
+    }
+
+    [Fact]
+    public void TargetIsType_HttpRequestDurationsMiddleware()
+    {
+        var app = new ApplicationBuilder(_services.BuildServiceProvider());
+        _services.AddSingleton<ICollectorRegistry, CollectorRegistry>();
+        app.UsePrometheusRequestDurations();
+
+        Assert.IsType<HttpRequestDurationsMiddleware>(app.Build().Target);
+    }
+
+    [Fact]
+    public void With_DefaultCollectorRegistry()
+    {
+        var app = new ApplicationBuilder(_services.BuildServiceProvider());
+        app.UsePrometheusRequestDurations();
+        app.Build();
+
+        Assert.True(Metrics.DefaultCollectorRegistry.TryGet(HttpRequestDurationsOptions.DefaultMetricName, out var defaultCollector));
+
+        // Cleanup
+        Metrics.DefaultCollectorRegistry?.Remove(defaultCollector);
+    }
+
+    [Fact]
+    public void With_DICollecorRegistry()
+    {
+        var registry = new CollectorRegistry();
+        _services.AddSingleton<ICollectorRegistry>(registry);
+        var app = new ApplicationBuilder(_services.BuildServiceProvider());
+        app.UsePrometheusRequestDurations();
+        app.Build();
+
+        Assert.True(registry.TryGet(HttpRequestDurationsOptions.DefaultMetricName, out _));
+
+        Assert.False(Metrics.DefaultCollectorRegistry.TryGet(HttpRequestDurationsOptions.DefaultMetricName, out _));
+    }
+
+    [Fact]
+    public void With_CustomCollecorRegistry()
+    {
+        var registry = new CollectorRegistry();
+
+        var app = new ApplicationBuilder(_services.BuildServiceProvider());
+        app.UsePrometheusRequestDurations(q => q.CollectorRegistry = registry);
+        app.Build();
+
+        Assert.True(registry.TryGet(HttpRequestDurationsOptions.DefaultMetricName, out _));
+
+        Assert.False(Metrics.DefaultCollectorRegistry.TryGet(HttpRequestDurationsOptions.DefaultMetricName, out _));
+    }
+}