How to use the @aws-sdk/util-buffer-from.fromString function in @aws-sdk/util-buffer-from

it(`should calculate a ${supportedHash} hmac of ${expected} for an input of ${data} and a key of ${key}`, async () => {
          const hash = new Hash(supportedHash, fromString(key, "hex"));
          hash.update(fromString(data, "hex"));
          const { buffer } = await hash.digest();
          expect(fromArrayBuffer(buffer).toString("hex")).toMatch(expected);
        });
      }

it(`should calculate a ${supportedHash} hash of ${expected} for an input of ${input}`, async () => {
          const hash = new Hash(supportedHash);
          hash.update(fromString(input, "base64"));
          const { buffer } = await hash.digest();
          expect(fromArrayBuffer(buffer).toString("hex")).toBe(expected);
        });
      }

it(`should calculate a ${supportedHash} hmac of ${expected} for an input of ${data} and a key of ${key}`, async () => {
          const hash = new Hash(supportedHash, fromString(key, "hex"));
          hash.update(fromString(data, "hex"));
          const { buffer } = await hash.digest();
          expect(fromArrayBuffer(buffer).toString("hex")).toMatch(expected);
        });
      }

export function fromUtf8(input: string): Uint8Array {
  const buf = fromString(input, "utf8");

  return new Uint8Array(
    buf.buffer,
    buf.byteOffset,
    buf.byteLength / Uint8Array.BYTES_PER_ELEMENT
  );
}

function castSourceData(toCast: SourceData, encoding?: string): Buffer {
  if (Buffer.isBuffer(toCast)) {
    return toCast;
  }

  if (typeof toCast === "string") {
    return fromString(toCast, encoding);
  }

  if (ArrayBuffer.isView(toCast)) {
    return fromArrayBuffer(toCast.buffer, toCast.byteOffset, toCast.byteLength);
  }

  return fromArrayBuffer(toCast);
}

export function fromBase64(input: string): Uint8Array {
  const buffer = fromString(input, "base64");

  return new Uint8Array(buffer.buffer, buffer.byteOffset, buffer.byteLength);
}