Add some tests and an input duplicate checker

types/psbt.d.ts

@@ -7,13 +7,14 @@ import { Transaction } from './transaction';
 export declare class Psbt extends PsbtBase {
     static fromTransaction<T extends typeof PsbtBase>(this: T, txBuf: Buffer): InstanceType<T>;
     static fromBuffer<T extends typeof PsbtBase>(this: T, buffer: Buffer): InstanceType<T>;
-    private __NON_WITNESS_UTXO_CACHE;
+    private __CACHE;
     private __TX;
     private __TX_BUF_CACHE?;
     private __FEE_RATE?;
     private __EXTRACTED_TX?;
     private opts;
     constructor(opts?: PsbtOptsOptional);
+    readonly inputCount: number;
     setMaximumFeeRate(satoshiPerByte: number): void;
     setVersion(version: number): this;
     setLocktime(locktime: number): this;