You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: op_alter_column_test.go
    path of file: ./repos/pgroll/pkg/migrations
    
    the code of the file until where you have to start completion: // SPDX-License-Identifier: Apache-2.0

package migrations_te
    
func TestAlterColumnValidation(t *testing.T) {
	t.Parallel()

	createTablesMigration := migrations.Migration{
		Name: "01_add_tables",
		Operations: migrations.Operations{
			&migrations.OpCreateTable{
				Name: "users",
				Columns: []migrations.Column{
					{
						Name: "id",
						Type: "serial",
						Pk:   ptr(true),
					},
					{
						Name: "name",
						Type: "text",
					},
				},
			},
			&migrations.OpCreateTable{
				Name: "posts",
				Columns: []migrations.Column{
					{
						Name: "id",
						Type: "serial",
						Pk:   ptr(true),
					},
					{
						Name: "title",
						Type: "text",
					},
					{
						Name: "user_id",
						Type: "integer",
					},
				},
			},
		},
	}

	ExecuteTests(t, TestCases{
		{
			name: "table must exist",
			migrations: []migrations.Migration{
				createTablesMigration,
				{
					Name: "01_alter_column",
					Operations: migrations.Operations{
						&migrations.OpAlterColumn{
							Table:  "doesntexist",
							Column: "title",
							Name:   ptr("renamed_title"),
						},
					},
				},
			},
			wantStartErr: migrations.TableDoesNotExistError{Name: "doesntexist"},
		},
		{
			name: "column must exist",
			migrations: []migrations.Migration{
				createTablesMigration,
				{
					Name: "01_alter_column",
					Operations: migrations.Operations{
						&migrations.OpAlterColumn{
							Table:  "posts",
							Column: "doesntexist",
							Name:   ptr("renamed_title"),
						},
					},
				},
			},
			wantStartErr: migrations.ColumnDoesNotExistError{Table: "posts", Name: "doesntexist"},
		},
		{
			name: "column rename: no up SQL allowed",
			migrations: []migrations.Migration{
				createTablesMigration,
				{
					Name: "01_alter_column",
					Operations: migrations.Operations{
						&migrations.OpAlterColumn{
							Table:  "posts",
							Column: "title",
							Name:   ptr("renamed_title"),
							Up:     ptr("some up sql"),
						},
					},
				},
			},
			wantStartErr: migrations.NoUpSQLAllowedError{},
		},
		{
			name: "column rename: no down SQL allowed",
			migrations: []migrations.Migration{
				createTablesMigration,
				{
					Name: "01_alter_column",
					Operations: migrations.Operations{
						&migrations.OpAlterColumn{
							Table:  "posts",
							Column: "title",
							Name:   ptr("renamed_title"),
							Down:   ptr("some down sql"),
						},
					},
				},
			},
			wantStartErr: migrations.NoDownSQLAllowedError{},
		},
		{
			name: "cant make no changes",
			migrations: []migrations.Migration{
				createTablesMigration,
				{
					Name: "01_alter_column",
					Operations: migrations.Operations{
						&migrations.OpAlterColumn{
							Table:  "posts",
							Column: "title",
						},
					},
				},
			},
			wantStartErr: migrations.MultipleAlterColumnChangesError{Changes: 0},
		},
		{
			name: "only one change at at time",
			migrations: []migrations.Migration{
				createTablesMigration,
				{
					Name: "01_alter_column",
					Operations: migrations.Operations{
						&migrations.OpAlterColumn{
							Table:  "posts",
							Column: "title",
							Name:   ptr("renamed_title"),
							Type:   ptr("varchar(255)"),
						},
					},
				},
			},
			wantStartErr: migrations.MultipleAlterColumnChangesError{Changes: 2},
		},
		{
			name: "table must have a primary key on exactly one column",
			migrations: []migrations.Migration{
				{
					Name: "01_add_table",
					Operations: migrations.Operations{
						&migrations.OpRawSQL{
							Up:   "CREATE TABLE orders(id integer, order_id integer, quantity integer, primary key (id, order_id))",
							Down: "DROP TABLE orders",
						},
					},
				},
				{
					Name: "02_alter_column",
					Operations: migrations.Operations{
						&migrations.OpAlterColumn{
							Table:  "orders",
							Column: "quantity",
							Name:   ptr("renamed_quantity"),
						},
					},
				},
			},
			wantStartErr: migrations.BackfillNotPossibleError{Table: "orders"},
		},
	})
}