[synthetics] Update docs to reflect the changes to expect (#3297)

* first draft switch to playwright expect

* adjust based on release notes

* clarify what's not supported

docs/en/observability/synthetics-create-test.asciidoc

@@ -155,42 +155,44 @@ For more details on getting started with the Synthetics Recorder, refer to <<syn
 == Playwright syntax
 
 Inside the callback for each step, you'll likely use a lot of Playwright syntax.
-Many Playwright classes are supported in the Elastic Synthetics library to simulate
-user workflows including tasks like:
+Use Playwright to simulate and validate user workflows including:
 
 * Interacting with the https://playwright.dev/docs/api/class-browser[browser]
   or the current https://playwright.dev/docs/api/class-page[page] (like in the example above).
 * Finding elements on a web page using https://playwright.dev/docs/api/class-locator[locators].
 * Simulating https://playwright.dev/docs/api/class-mouse[mouse],
   https://playwright.dev/docs/api/class-touchscreen[touch], or
   https://playwright.dev/docs/api/class-keyboard[keyboard] events.
+* Making assertions using https://playwright.dev/docs/test-assertions[`@playwright/test`'s `expect` function]. Read more in <<synthetics-make-assertions>>.
 
 Visit the https://playwright.dev/docs[Playwright documentation] for information.
 
 However, not all Playwright functionality should be used with Elastic Synthetics.
-
 In some cases, there are alternatives to Playwright functionality built into the
 Elastic Synthetics library. These alternatives are designed to work better for
 synthetic monitoring. Do _not_ use Playwright syntax to:
 
-* *Make assertions*. Use Elastic Synthetics's `expect` methods instead.
-  Read more in <<synthetics-make-assertions>>.
 * *Make API requests.* Use Elastic Synthetic's `request`
   parameter instead. Read more in <<synthetics-request-param>>.
 
 There is also some Playwright functionality that is not supported out-of-the-box
 in Elastic Synthetics including:
 
 * https://playwright.dev/docs/api/class-video[Videos]
+* The https://playwright.dev/docs/api/class-locatorassertions#locator-assertions-to-have-screenshot-1[`toHaveScreenshot`] and https://playwright.dev/docs/api/class-snapshotassertions[`toMatchSnapshot`] assertions
 
 [discrete]
 [[synthetics-make-assertions]]
 = Make assertions
 
-Check that a value meets a specific condition.
 A more complex `step` might wait for a page element to be selected
 and then make sure that it matches an expected value.
 
+Elastic Synthetics uses `@playwright/test`'s `expect` function to make assertions
+and supports most https://playwright.dev/docs/test-assertions[Playwright assertions].
+Elastic Synthetics does _not_ support https://playwright.dev/docs/api/class-locatorassertions#locator-assertions-to-have-screenshot-1[`toHaveScreenshot`]
+or any https://playwright.dev/docs/api/class-snapshotassertions[Snapshot Assertions].
+
 For example, on a page using the following HTML:
 
 [source,html]
@@ -219,38 +221,6 @@ step('Assert placeholder text', async () => {
 <2> Use the assertion library provided by the Synthetics agent to check that
 the value of the `placeholder` attribute matches a specific string.
 
-[discrete]
-[[synthetics-assertions-methods]]
-== Supported `expect` methods
-
-:jest: https://jestjs.io/docs
-
-* {jest}/expect#not[`not ()`]
-* {jest}/expect#resolves[`resolves ()`]
-* {jest}/expect#rejects[`rejects ()`]
-* {jest}/expect#tobevalue[`toBe (expected)`]
-* {jest}/expect#tobeclosetonumber-numdigits[`toBeCloseTo (expected, numDigits?)`]
-* {jest}/expect#tobedefined[`toBeDefined ()`]
-* {jest}/expect#tobefalsy[`toBeFalsy ()`]
-* {jest}/expect#tobegreaterthannumber\--bigint[`toBeGreaterThan (expected)`]
-* {jest}/expect#tobegreaterthanorequalnumber\--bigint[`toBeGreaterThanOrEqual (expected)`]
-* {jest}/expect#tobeinstanceofclass[`toBeInstanceOf (expected)`]
-* {jest}/expect#tobelessthannumber\--bigint[`toBeLessThan (expected)`]
-* {jest}/expect#tobelessthanorequalnumber\--bigint[`toBeLessThanOrEqual (expected)`]
-* {jest}/expect#tobenull[`toBeNull ()`]
-* {jest}/expect#tobetruthy[`toBeTruthy ()`]
-* {jest}/expect#tobeundefined[`toBeUndefined ()`]
-* {jest}/expect#tobenan[`toBeNaN ()`]
-* {jest}/expect#tocontainitem[`toContain (expected)`]
-* {jest}/expect#tocontainequalitem[`toContainEqual (expected)`]
-* {jest}/expect#toequalvalue[`toEqual (expected)`]
-* {jest}/expect#tohavelengthnumber[`toHaveLength (expected)`]
-* {jest}/expect#tohavepropertykeypath-value[`toHaveProperty (keyPath, value?)`]
-* {jest}/expect#tomatchregexp\--string[`toMatch (expected)`]
-* {jest}/expect#tomatchobjectobject[`toMatchObject (expected)`]
-* {jest}/expect#tostrictequalvalue[`toStrictEqual (expected)`]
-
-
 [discrete]
 [[synthetics-request-param]]
 = Make API requests