public NullKeysSqliteFixture()
{
var serviceProvider = new ServiceCollection()
.AddEntityFrameworkSqlite()
.AddSingleton(TestModelSource.GetFactory(OnModelCreating))
.BuildServiceProvider(validateScopes: true);
_options = new DbContextOptionsBuilder()
.UseSqlite(SqliteTestStore.CreateConnectionString("StringsContext"))
.UseInternalServiceProvider(serviceProvider)
.Options;
CreateContext().Database.EnsureClean();
EnsureCreated();
}