fix: Throw an exception if the container has exited while checking for readiness

Fixes #1445

Author: 0xced

src/Testcontainers/Configurations/WaitStrategies/ContainerException.cs

@@ -0,0 +1,21 @@
+using System;
+using JetBrains.Annotations;
+
+namespace DotNet.Testcontainers.Configurations
+{
+  /// <summary>
+  /// Represents an exception that is thrown when a Docker container fails to start.
+  /// </summary>
+  [PublicAPI]
+  public sealed class ContainerException : Exception
+  {
+    /// <summary>
+    /// Initializes a new instance of the <see cref="ContainerException" /> class.
+    /// </summary>
+    /// <param name="message">The message that describes the error.</param>
+    public ContainerException(string message)
+      : base(message)
+    {
+    }
+  }
+}

src/Testcontainers/Containers/DockerContainer.cs

@@ -5,6 +5,7 @@ namespace DotNet.Testcontainers.Containers
   using System.Globalization;
   using System.IO;
   using System.Linq;
+  using System.Text;
   using System.Threading;
   using System.Threading.Tasks;
   using Docker.DotNet;
@@ -635,6 +636,9 @@ private async Task<bool> CheckReadinessAsync(WaitStrategy waitStrategy, Cancella
       _container = await _client.Container.ByIdAsync(_container.ID, ct)
         .ConfigureAwait(false);
 
+      await ThrowIfExitedAsync(ct)
+        .ConfigureAwait(false);
+
       return await waitStrategy.UntilAsync(this, ct)
         .ConfigureAwait(false);
     }
@@ -660,6 +664,39 @@ await WaitStrategy.WaitUntilAsync(() => CheckReadinessAsync(waitStrategy, ct), w
       return true;
     }
 
+    private async Task ThrowIfExitedAsync(CancellationToken ct = default)
+    {
+      if (State == TestcontainersStates.Exited)
+      {
+        var message = new StringBuilder($"The {Image.FullName} container has exited.");
+        try
+        {
+          var (stdout, stderr) = await GetLogsAsync(ct: ct)
+            .ConfigureAwait(false);
+
+          stdout = stdout.Trim();
+          stderr = stderr.Trim();
+
+          message.AppendLine();
+
+          if (stderr.Length > 0)
+          {
+            message.AppendLine().AppendLine($"=== stderr of {Name.TrimStart('/')} ({Id}) ===").AppendLine(stderr);
+          }
+
+          if (stdout.Length > 0)
+          {
+            message.AppendLine().AppendLine($"=== stdout of {Name.TrimStart('/')} ({Id}) ===").AppendLine(stdout);
+          }
+        }
+        catch
+        {
+          message.AppendLine(" Please look at the container logs.");
+        }
+        throw new ContainerException(message.ToString());
+      }
+    }
+
     private sealed class WaitUntilPortBindingsMapped : WaitStrategy
     {
       private readonly DockerContainer _parent;

tests/Testcontainers.Platform.Linux.Tests/DependsOnTest.cs

@@ -19,11 +19,13 @@ public async ValueTask InitializeAsync()
     {
         var childContainer1 = new ContainerBuilder()
             .WithImage(CommonImages.Alpine)
+            .WithEntrypoint(CommonCommands.SleepInfinity)
             .WithLabel(_labelKey, _labelValue)
             .Build();
 
         var childContainer2 = new ContainerBuilder()
             .WithImage(CommonImages.Alpine)
+            .WithEntrypoint(CommonCommands.SleepInfinity)
             .WithLabel(_labelKey, _labelValue)
             .Build();
 
@@ -41,6 +43,7 @@ public async ValueTask InitializeAsync()
             .DependsOn(network)
             .DependsOn(volume, "/workdir")
             .WithImage(CommonImages.Alpine)
+            .WithEntrypoint(CommonCommands.SleepInfinity)
             .WithLabel(_labelKey, _labelValue)
             .Build();