How to use the chai.assert.isFunction function in chai

it('should be a function', () => {
    assert.isFunction(show)
  })

it("should have the createServer method", function () {
        assert.isFunction(server.createServer);
    });
});

it("should generate the body and Window property", () => {
          const dom = createJSDOM();
          dom.window.document.body.setAttribute("onhashchange", "document.body.onhashchangeRan = true;");

          assert.isFunction(dom.window.document.body.onhashchange);
          assert.isFunction(dom.window.onhashchange);
          assert.strictEqual(dom.window.document.body.onhashchange, dom.window.onhashchange);
        });

it('should be a function', () => {
                assert.isFunction(cpu.thisLoad);
            });

it('should be a function', () => {
    assert.isFunction(getWidth)
  })

it('exports a function', () => {
		assert.isFunction(cleanModulesParameter);
	});

it('should have function $$PREBID_GLOBAL$$.getAllWinningBids', function () {
      assert.isFunction($$PREBID_GLOBAL$$.getAllWinningBids);
    });
  });

collectFees: function (p) {
      assert.deepEqual(p.branch, '0xb1');
      assert.deepEqual(p.sender, '0x1');
      assert.deepEqual(p.periodLength, 1000);
      assert.isFunction(p.onSent);
      assert.isFunction(p.onSuccess);
      assert.isFunction(p.onFailed);

      p.onSent('1');
      p.onSuccess('1');
    }
  });

acc.contacts.forEach(contact => {
      assert.isFunction(contact.update, 'Child Objects Should have DML functions!');
      assert.isFunction(contact.insert, 'Child Objects Should have DML functions!');
      assert.isFunction(contact.delete, 'Child Objects Should have DML functions!');
    });
  }

DataFrame.prototype.aggregate = function (seedOrSelector, selector) {

	var self = this;

	if (Object.isFunction(seedOrSelector) && !selector) {
		return self.skip(1).aggregate(self.first(), seedOrSelector);
	}
	else if (selector) {
		assert.isFunction(selector, "Expected 'selector' parameter to aggregate to be a function.");

		var working = seedOrSelector;
		var it = self.iterable.getIterator();
		while (it.moveNext()) {
			var curValue = it.getCurrent()[1];
			working = selector(working, curValue);
		}

		return working;		
	}
	else {
		assert.isObject(seedOrSelector, "Expected 'seed' parameter to aggregate to be an object.");

		return E.from(Object.keys(seedOrSelector))
			.select(function (columnName) {
				var columnSelector = seedOrSelector[columnName];