Add RequiresDocker trait to database test collections

tests/Bravellian.Platform.Postgres.Tests/PostgresCollection.cs

@@ -19,6 +19,7 @@ namespace Bravellian.Platform.Tests;
 /// Tests in this collection will share the same PostgreSQL container but get individual databases.
 /// </summary>
 [CollectionDefinition(Name)]
+[Trait("RequiresDocker", "true")]
 public class PostgresCollection : ICollectionFixture<PostgresCollectionFixture>
 {
     public const string Name = "Postgres Collection";

tests/Bravellian.Platform.Tests/SqlServerCollection.cs

@@ -19,6 +19,7 @@ namespace Bravellian.Platform.Tests;
 /// Tests in this collection will share the same SQL Server container but get individual databases.
 /// </summary>
 [CollectionDefinition(Name)]
+[Trait("RequiresDocker", "true")]
 public class SqlServerCollection : ICollectionFixture<SqlServerCollectionFixture>
 {
     public const string Name = "SQL Server Collection";

tests/Bravellian.Platform.Tests/SqlServerCollectionFixture.cs

@@ -112,6 +112,10 @@ public async Task<string> CreateTestDatabaseAsync(string name)
 
     internal void EnsureAvailable()
     {
+        if (!isAvailable)
+        {
+            throw new InvalidOperationException("SQL Server tests cannot run because sqlcmd is not available. Install SQL Server command-line tools to run these tests.");
+        }
     }
 }