testcases:
  - name: "testcase 1"
    inputs:
    - 1 : ["push", "pop", "push", "pop"]
    - 2 : [14, null, 66, null]
    output: 
    - 1 : [null, 14, null, 66]
  - name: "testcase 2"
    inputs:
    - 1: ["push", "peek"]
    - 2: [4, null]
    output:
    - 1 : [null, 4]
  - name: "testcase 3"
    inputs:
    - 1 : ["push", "push", "push", "pop", "peek", "empty"]
    - 2 : [9, 3, 1, null, null, null]
    output: 
    - 1 : [null, null, null, 9, 3, False]
  - name: "testcase 4"
    inputs:
    - 1: ["push", "push", "pop", "empty", "peek"]
    - 2: [10, 6, null, null, null]
    output:
    - 1 : [null, null, 10, False, 6]
  - name: "testcase 5"
    inputs:
    - 1: ["push", "push","push", "peek", "pop", "pop", "pop", "empty"]
    - 2: [1, 2, 3, null, null, null, null, null]
    output:
    - 1 : [null, null, null, 1, 1, 2, 3, True]