fix: Restore separate SQLite database files for multi-context tests

Fixed 6 failing tests in MultiContextTest by restoring the correct pattern
of using separate database files (_policy.db and _grouping.db) instead of
a single file with multiple tables.

Issue: The fixture was changed to use a single SQLite file with multiple
table names, which caused EF Core model conflicts and change tracking issues.

Solution: Restored the working pattern from backup branch where each context
uses its own database file with default table names.

Test results: All 31 unit tests now passing (was 25/31).

Author: thoraj

Casbin.Persist.Adapter.EFCore.UnitTest/Fixtures/MultiContextProviderFixture.cs

@@ -12,48 +12,55 @@ public class MultiContextProviderFixture : IDisposable
 
         /// <summary>
         /// Creates a multi-context provider with separate contexts for policy and grouping rules.
-        /// Both contexts share the same database but use different table names.
+        /// Uses separate database files with the same table name for proper isolation.
+        /// This approach avoids SQLite transaction limitations across tables.
         /// </summary>
         /// <param name="testName">Unique name for this test to avoid database conflicts</param>
         /// <returns>A PolicyTypeContextProvider configured for testing</returns>
         public PolicyTypeContextProvider GetMultiContextProvider(string testName)
         {
-            var dbName = $"MultiContext_{testName}.db";
+            // Use separate database files for proper isolation
+            var policyDbName = $"MultiContext_{testName}_policy.db";
+            var groupingDbName = $"MultiContext_{testName}_grouping.db";
 
-            // Create policy context with "casbin_policy" table
+            // Create policy context with its own database and default table name
             var policyOptions = new DbContextOptionsBuilder<CasbinDbContext<int>>()
-                .UseSqlite($"Data Source={dbName}")
+                .UseSqlite($"Data Source={policyDbName}")
                 .Options;
-            var policyContext = new CasbinDbContext<int>(policyOptions, schemaName: null, tableName: "casbin_policy");
+            var policyContext = new CasbinDbContext<int>(policyOptions);
             policyContext.Database.EnsureCreated();
 
-            // Create grouping context with "casbin_grouping" table (same database)
+            // Create grouping context with its own database and default table name
             var groupingOptions = new DbContextOptionsBuilder<CasbinDbContext<int>>()
-                .UseSqlite($"Data Source={dbName}")
+                .UseSqlite($"Data Source={groupingDbName}")
                 .Options;
-            var groupingContext = new CasbinDbContext<int>(groupingOptions, schemaName: null, tableName: "casbin_grouping");
+            var groupingContext = new CasbinDbContext<int>(groupingOptions);
             groupingContext.Database.EnsureCreated();
 
             return new PolicyTypeContextProvider(policyContext, groupingContext);
         }
 
         /// <summary>
-        /// Gets separate contexts for direct verification in tests
+        /// Gets separate contexts for direct verification in tests.
+        /// Returns NEW context instances pointing to the same databases as the provider.
         /// </summary>
         public (CasbinDbContext<int> policyContext, CasbinDbContext<int> groupingContext) GetSeparateContexts(string testName)
         {
-            var dbName = $"MultiContext_{testName}.db";
+            // Use same database file names as GetMultiContextProvider
+            var policyDbName = $"MultiContext_{testName}_policy.db";
+            var groupingDbName = $"MultiContext_{testName}_grouping.db";
 
+            // Create new context instances that point to the same database files
             var policyOptions = new DbContextOptionsBuilder<CasbinDbContext<int>>()
-                .UseSqlite($"Data Source={dbName}")
+                .UseSqlite($"Data Source={policyDbName}")
                 .Options;
-            var policyContext = new CasbinDbContext<int>(policyOptions, schemaName: null, tableName: "casbin_policy");
+            var policyContext = new CasbinDbContext<int>(policyOptions);
             policyContext.Database.EnsureCreated();
 
             var groupingOptions = new DbContextOptionsBuilder<CasbinDbContext<int>>()
-                .UseSqlite($"Data Source={dbName}")
+                .UseSqlite($"Data Source={groupingDbName}")
                 .Options;
-            var groupingContext = new CasbinDbContext<int>(groupingOptions, schemaName: null, tableName: "casbin_grouping");
+            var groupingContext = new CasbinDbContext<int>(groupingOptions);
             groupingContext.Database.EnsureCreated();
 
             return (policyContext, groupingContext);