Add GetEnvironmentVariableValuesAsync method to ResourceExtensions

src/Aspire.Hosting/ApplicationModel/ResourceExtensions.cs

@@ -65,6 +65,78 @@ public static bool TryGetEnvironmentVariables(this IResource resource, [NotNullW
         return TryGetAnnotationsOfType(resource, out environmentVariables);
     }
 
+    /// <summary>
+    ///  Get the environment variables from the given resource.
+    /// </summary>
+    /// <remarks>
+    /// This method is useful when you want to make sure the environment variables are added properly to resources, mostly in test situations.
+    /// This method has asynchronous behavior if <paramref name = "applicationOperation" /> be <see cref="DistributedApplicationOperation.Run"/>
+    /// and environment variables were provided from <see cref="IValueProvider"/> otherwise it will be synchronous.
+    /// </remarks>
+    /// <param name="resource">The resource to get the environment variables from.</param>
+    /// <param name="applicationOperation">The context in which the AppHost is being executed</param>
+    /// <returns>The environment variables retrieved from the resource.</returns>
+    /// <example>
+    /// <code>
+    /// using var builder = TestDistributedApplicationBuilder.Create();
+    ///
+    /// builder.AddMongoDB("mongo")
+    ///      .WithEndpoint("tcp", e => e.AllocatedEndpoint = new AllocatedEndpoint(e, "localhost", 3000, containerHost))
+    ///      .WithMongoExpress();
+    ///
+    ///   var env = await mongoExpress.GetEnvironmentVariableValuesAsync();
+    ///
+    ///   Assert.Collection(env,
+    ///       e =>
+    ///           {
+    ///               Assert.Equal("ME_CONFIG_MONGODB_URL", e.Key);
+    ///               Assert.Equal($"mongodb://{containerHost}:3000/?directConnection=true", e.Value);
+    ///           },
+    ///           e =>
+    ///           {
+    ///               Assert.Equal("ME_CONFIG_BASICAUTH", e.Key);
+    ///               Assert.Equal("false", e.Value);
+    ///           });
+    /// </code>
+    /// </example>
+
+    public static async ValueTask<IReadOnlyDictionary<string, string>> GetEnvironmentVariableValuesAsync(this IResourceWithEnvironment resource,
+            DistributedApplicationOperation applicationOperation = DistributedApplicationOperation.Run)
+    {
+        var environmentVariables = new Dictionary<string, string>();
+
+        if (resource.TryGetEnvironmentVariables(out var callbacks))
+        {
+            var config = new Dictionary<string, object>();
+            var executionContext = new DistributedApplicationExecutionContext(applicationOperation);
+            var context = new EnvironmentCallbackContext(executionContext, config);
+
+            foreach (var callback in callbacks)
+            {
+                await callback.Callback(context).ConfigureAwait(false);
+            }
+
+            foreach (var (key, expr) in config)
+            {
+                var value = (applicationOperation, expr) switch
+                {
+                    (_, string s) => s,
+                    (DistributedApplicationOperation.Run, IValueProvider provider) => await provider.GetValueAsync().ConfigureAwait(false),
+                    (DistributedApplicationOperation.Publish, IManifestExpressionProvider provider) => provider.ValueExpression,
+                    (_, null) => null,
+                    _ => throw new InvalidOperationException($"Unsupported expression type: {expr.GetType()}")
+                };
+
+                if (value is not null)
+                {
+                    environmentVariables[key] = value;
+                }
+            }
+        }
+
+        return environmentVariables;
+    }
+
     /// <summary>
     /// Attempts to get the container mounts for the specified resource.
     /// </summary>

src/Aspire.Hosting/PublicAPI.Unshipped.txt

@@ -1,4 +1,5 @@
 #nullable enable
+static Aspire.Hosting.ApplicationModel.ResourceExtensions.GetEnvironmentVariableValuesAsync(this Aspire.Hosting.ApplicationModel.IResourceWithEnvironment! resource, Aspire.Hosting.DistributedApplicationOperation applicationOperation = Aspire.Hosting.DistributedApplicationOperation.Run) -> System.Threading.Tasks.ValueTask<System.Collections.Generic.IReadOnlyDictionary<string!, string!>!>
 Aspire.Hosting.ApplicationModel.ResourceNotificationService.ResourceNotificationService(Microsoft.Extensions.Logging.ILogger<Aspire.Hosting.ApplicationModel.ResourceNotificationService!>! logger, Microsoft.Extensions.Hosting.IHostApplicationLifetime! hostApplicationLifetime) -> void
 Aspire.Hosting.ApplicationModel.ResourceNotificationService.WaitForResourceAsync(string! resourceName, string? targetState = null, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> System.Threading.Tasks.Task!
 Aspire.Hosting.ApplicationModel.ResourceNotificationService.WaitForResourceAsync(string! resourceName, System.Collections.Generic.IEnumerable<string!>! targetStates, System.Threading.CancellationToken cancellationToken = default(System.Threading.CancellationToken)) -> System.Threading.Tasks.Task<string!>!