feat: 🎸 add method: QuorumTestLedger#getGenesisAccount()

A utility method on to easily obtain an account from the genesis
allocation that has a high balance to seed other accounts without having
to mine for them (which doesn't make sense in a quorom ledger for us in
a testing environment)

Signed-off-by: Peter Somogyvari <peter.somogyvari@accenture.com>

packages/cactus-test-tooling/src/main/typescript/quorum/quorum-test-ledger.ts

@@ -105,6 +105,25 @@ export class QuorumTestLedger implements ITestLedger {
     });
   }
 
+  /**
+   * Obtains the address of an account from the genesis allocation with a
+   * minimum balance of `minBalance`.
+   *
+   * @param minBalance The minimum balance to try and find a genesis account with.
+   *
+   * @throws {Error} If the balance is too high and there aren't any genesis
+   * accounts allocated with such a high balance then an exceptin is thrown.
+   */
+  public async getGenesisAccount(minBalance: number = 10e7): Promise<string> {
+    const { alloc } = await this.getGenesisJsObject();
+
+    const firstHighNetWorthAccount = Object.keys(alloc).find(
+      (addr) => parseInt(alloc[addr].balance, 10) > minBalance
+    ) as string;
+
+    return firstHighNetWorthAccount;
+  }
+
   public async getQuorumKeyPair(): Promise<IKeyPair> {
     const publicKey = await this.getFileContents("/nodekey");
     const privateKey = await this.getFileContents("/key");