Add balancesOf method to MRC20 contract and corresponding tests

src/contracts-wrappers/token.ts

@@ -1,4 +1,4 @@
-import { Args, bytesToStr, U256, U8 } from '../basicElements'
+import { Args, bytesToStr, strToBytes, U256, U8 } from '../basicElements'
 import { Operation } from '../operation'
 import { CallSCOptions, ReadSCOptions, SmartContract } from '../smartContracts'
 
@@ -85,6 +85,24 @@ export class MRC20 extends SmartContract {
     return U256.fromBytes(res.value)
   }
 
+  async balancesOf(addresses: string[]): Promise<
+    {
+      address: string
+      balance: bigint
+    }[]
+  > {
+    const res = await this.provider.readStorage(
+      this.address,
+      addresses.map((a) => strToBytes(`BALANCE${a}`)),
+      true
+    )
+
+    return res.map((v, i) => ({
+      address: addresses[i],
+      balance: v.length ? U256.fromBytes(v) : 0n,
+    }))
+  }
+
   async transfer(
     to: string,
     amount: bigint,

test/integration/MRC20.spec.ts

@@ -1,3 +1,4 @@
+import { account, Account } from '../../src'
 import { MRC20 } from '../../src/contracts-wrappers'
 import { provider } from './setup'
 
@@ -80,4 +81,35 @@ describe('Generic token wrapper tests', () => {
     )
     expect(newAllowance).toBe(previousAllowance)
   })
+
+  test('balancesOf', async () => {
+    const amounts = [1_000n, 2_000n]
+    const recipientAddresses = [
+      await (await Account.generate()).address.toString(),
+      await (await Account.generate()).address.toString(),
+    ]
+
+    const b = await usdcContract.balancesOf(recipientAddresses)
+    for (const { address, balance } of b) {
+      expect(balance).toBe(0n)
+    }
+
+    const operation = await usdcContract.transfer(
+      recipientAddresses[0],
+      amounts[0]
+    )
+
+    const operation2 = await usdcContract.transfer(
+      recipientAddresses[1],
+      amounts[1]
+    )
+    await operation2.waitFinalExecution()
+
+    const recipientBalance = await usdcContract.balancesOf(recipientAddresses)
+
+    expect(recipientBalance[0].balance).toBe(amounts[0])
+    expect(recipientBalance[0].address).toBe(recipientAddresses[0])
+    expect(recipientBalance[1].balance).toBe(amounts[1])
+    expect(recipientBalance[1].address).toBe(recipientAddresses[1])
+  })
 })