knexSnakeCaseMappers with underscoreBeforeDigits

[bilalakbar]

Hello,

I needed some clarification regarding the behavior of knexSnakeCaseMappers({ underscoreBeforeDigits: true }) introduced after this issue #1025.
We are using knex for migrations and objection as ORM in our codebase. When using Objection we use camelCase and in Knex migrations we use snake_case for table and column names. This is what our knex config looks like

const knexConfig: Knex.Config = {
  client: 'postgresql',
  connection: 'connection url string',
  pool: {
    min: 0,
    max: 10
  },
  migrations: {
    tableName: 'knex_migrations',
    directory: '../migrations'
  },
  ...knexSnakeCaseMappers({ underscoreBeforeDigits: true })
};

However, the problem is when we already pass a snake_case string and underscoreBeforeDigits is true, it adds an additional underscore before the number.
For example, we have a migration like this

export async function up(knex: Knex): Promise<void> {
  await knex.schema.createTable('test_2_tables', (tb) => {
	// create columns
  });

When we run this migration, the table is created with name test__2_tables (notice the double underscore before 2).

Is this expected behavior of this function ?
Personally, I don't think so, because it does not add double underscore everywhere else.

I have created a draft PR with possible fix and added a test cases for that.

#2804