How to use clearSessions method in Cypress

Just like Alex mentioned in the comment, you cannot return a value from cy commands. But you can do so in the .then block just like:

 it("should have text of 'Backpack'", () => {

  // I have changed the selector since the class name in your HTML is ".inventory_item_name" not ".inventory_item_price"
  cy.get(".inventory_item_name").then(($el) => {
    const text = $el.text(); // Now you have the text "Backpack"

    // Do the assertion here
    expect(text).to.eq("Backpack");
  });
});

You can learn more about why Cypress doesn't return value in this documentation

This works to check a count of items:

cy.get('.Button_Container').find('button').should('have.length', 3)

or

cy.get('.Button_Container').find('button').its('length').should('eq', 3)

I would first check the "in progress" status to ensure the sequence is correct.

cy.contains('tbody tr:eq(0)', 'in progress')
cy.contains('tbody tr:eq(0)', 'complete', {timeout:300000})

Yes, there is. Cypress is actually running in the browser, and although commands are queued asynchronously, you can queue up native JS code to be run, like so:

cy.get("html").then(() => {
    document.querySelector("div.myDiv").innerHTML = "...";
    // ...
});

If you are trying to target or modify a specific element, you can get it via Cypress to take advantage of automatic retries to wait for the element to exist before operating on it:

cy.get("div.myDiv").then(elem => {
    elem.innerHTML = "...";
    // ...
});

As you stated in your question there is not difference between cy.get("a").find("b") and cy.get("a b"). But the most important difference between find and get commands in Cypress is that cy.get() is chained off of cy, it always looks for the selector within the entire document as stated in Cypress documents. But as again stated in Cypress documents find works as follows:

Get the descendent DOM elements of a specific selector.

So the command cy.get("a").find("b") returns all the b elements which are successor of an a element, but cy.get("a").get("b") finds all the a and b elements regardless of they are parent and child.

I think you are using the wrong quotes, you need to use backticks to use Template Literals:

cy.visit(`http://test.com/aaa/bbb?id=${idp}`)

You can then use cy.url() to get the current URL as a string and use JavaScript to parse the string as normal.

You need to tell Typescript that some of parameters are optional:

// index.d.ts
declare namespace Cypress {
  interface JQuery<HTMLElement> {
    rsChoose(text?, num?, all?): JQuery<HTMLElement>
  }
}

Also if you use Typescript I recommend you to add types to your parameters ;)

This seems to work folks. I believe initial !important is a reference of some sort and not an actual value and maybe that's why .css() wouldn't work.

Cypress.Commands.add('hideHubSpot', () => {
    cy.get('#hubspot-messages-iframe-container')
        .invoke('attr', 'style', 'display: none')
        .should('have.attr', 'style', 'display: none')

You have to use then() instead of should() -

cy.get('p.text-lg').invoke('text').then((text) => {
    var splitText = text.split(' ')[5]
    expect(splitText).to.equal(291)
})