"phase tester" meaning in English

{
  "forms": [
    {
      "form": "phase testers",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "phase tester (plural phase testers)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English entries with topic categories using raw markup",
          "parents": [
            "Entries with topic categories using raw markup",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English terms with non-redundant non-automated sortkeys",
          "parents": [
            "Terms with non-redundant non-automated sortkeys",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Tools",
          "orig": "en:Tools",
          "parents": [
            "Technology",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "A device, often built into a screwdriver, used to check for electric current."
      ],
      "id": "en-phase_tester-en-noun-QWch8l2W",
      "links": [
        [
          "device",
          "device"
        ],
        [
          "screwdriver",
          "screwdriver"
        ]
      ]
    }
  ],
  "word": "phase tester"
}

{
  "forms": [
    {
      "form": "phase testers",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "phase tester (plural phase testers)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English entries with topic categories using raw markup",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English terms with non-redundant non-automated sortkeys",
        "en:Tools"
      ],
      "glosses": [
        "A device, often built into a screwdriver, used to check for electric current."
      ],
      "links": [
        [
          "device",
          "device"
        ],
        [
          "screwdriver",
          "screwdriver"
        ]
      ]
    }
  ],
  "word": "phase tester"
}