Simple clone impl only on PGlite (#526)

* simple clone impl on PGlite

---------

Co-authored-by: tudor <[email protected]>

.changeset/mighty-grapes-refuse.md

@@ -0,0 +1,5 @@
+---
+'@electric-sql/pglite': patch
+---
+
+added clone() method to pglite API. clones an instance such that it can be reused (for example running tests on existing data without readding all data)

docs/docs/api.md

@@ -361,6 +361,11 @@ await pg.describeQuery('SELECT * FROM test WHERE name = $1', ['test'])
 }
 ```
 
+### clone
+`.clone(): Promise<PGlite>`
+
+Clones the current instance. This is useful when a series of operations, like unit or integration test, need to be run on the same database without having to recreate the database each time, or for each test. 
+
 ## Properties
 
 ### ready

packages/pglite/src/pglite.ts

@@ -794,4 +794,9 @@ export class PGlite
   _runExclusiveTransaction<T>(fn: () => Promise<T>): Promise<T> {
     return this.#transactionMutex.runExclusive(fn)
   }
+
+  async clone(): Promise<PGliteInterface> {
+    const dump = await this.dumpDataDir('none')
+    return new PGlite({ loadDataDir: dump })
+  }
 }

packages/pglite/tests/clone.test.js

@@ -0,0 +1,42 @@
+import { describe, it, expect } from 'vitest'
+import { PGlite } from '../dist/index.js'
+
+describe('clone', () => {
+  it('clone pglite instance', async () => {
+    const pg1 = new PGlite()
+    await pg1.exec(`
+    CREATE TABLE IF NOT EXISTS test (
+      id SERIAL PRIMARY KEY,
+      name TEXT
+    );
+  `)
+    await pg1.exec("INSERT INTO test (name) VALUES ('test');")
+
+    const pg2 = await pg1.clone()
+
+    const ret1 = await pg1.query('SELECT * FROM test;')
+    const ret2 = await pg2.query('SELECT * FROM test;')
+
+    expect(ret1).toEqual(ret2)
+  })
+
+  it('clone pglite instance - insert into pg2', async () => {
+    const pg1 = new PGlite()
+    await pg1.exec(`
+    CREATE TABLE IF NOT EXISTS test (
+      id SERIAL PRIMARY KEY,
+      name TEXT
+    );
+  `)
+    await pg1.exec("INSERT INTO test (name) VALUES ('test');")
+
+    const pg2 = await pg1.clone()
+    await pg2.exec("INSERT INTO test (name) VALUES ('2-test');")
+
+    const ret1 = await pg1.query('SELECT * FROM test;')
+    const ret2 = await pg2.query('SELECT * FROM test;')
+
+    expect(ret1.rows.length).toBe(1)
+    expect(ret2.rows.length).toBe(2)
+  })
+})