add non-breaking space tests

cypress/integration/non-breaking-space.md

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+# Non-breaking space
+
+Dealing with ` ` character aka [Non-breaking space](https://en.wikipedia.org/wiki/Non-breaking_space).
+
+When using [cy.contains](https://on.cypress.io/contains) command Cypress automatically converts the ` ` entity into space character. Thus `cy.contains` finds element that include ` `.
+
+<!-- fiddle Without whitespace -->
+```html
+<div data-testid="testattr">
+  <div><span>GBP 0.50</span></div>
+</div>
+```
+
+```js
+// both commands work
+cy.contains ('[data-testid=testattr]', 'GBP 0.50').should('be.visible')
+cy.get('[data-testid=testattr]')
+  .filter(':contains("GBP 0.50")')
+  .should('have.length', 1)
+```
+<!-- fiddle-end -->
+
+But if the HTML contains the whitespace special character `&nbsp;` then checking elements by text is tricky. See [#9530](https://github.com/cypress-io/cypress/issues/9530) for example. This is because [.filter](https://on.cypress.io/filter) uses jQuery [:contains selector](https://api.jquery.com/contains-selector/) which uses literal text match.
+
+<!-- fiddle With whitespace / cy.contains works -->
+```html
+<div data-testid="testattr">
+  <div><span>GBP&nbsp;0.50</span></div>
+</div>
+```
+
+```js
+cy.contains ('[data-testid=testattr]', 'GBP 0.50').should('be.visible')
+```
+<!-- fiddle-end -->
+
+<!-- fiddle With whitespace / use Unicode in .filter -->
+```html
+<div data-testid="testattr">
+  <div><span>GBP&nbsp;0.50</span></div>
+</div>
+```
+
+```js
+// we can filter by text before the &nbsp;
+cy.get('[data-testid=testattr]')
+  .filter(':contains("GBP")')
+  .should('have.length', 1)
+
+cy.get('[data-testid=testattr]')
+  // the following filter DOES NOT WORK
+  // .filter(':contains("GBP 0.50")')
+  // the following filter DOES NOT WORK
+  // .filter(':contains("GBP&nbsp;0.50")')
+  // but the Unicode representation of non-breaking space character works
+  .filter(':contains("GBP\u00a00.50")')
+  .should('have.length', 1)
+```
+<!-- fiddle-end -->
+
+## Result
+
+![Non-breaking space tests](../../images/non-breaking-space.png)