Testing: Add E2E case to ensure cleaned TinyMCE content

test/e2e/specs/__snapshots__/writing-flow.test.js.snap

@@ -24,6 +24,18 @@ exports[`adding blocks Should navigate inner blocks with arrow keys 1`] = `
 <!-- /wp:paragraph -->"
 `;
 
+exports[`adding blocks should clean TinyMCE content 1`] = `
+"<!-- wp:paragraph -->
+<p><strong></strong></p>
+<!-- /wp:paragraph -->"
+`;
+
+exports[`adding blocks should clean TinyMCE content 2`] = `
+"<!-- wp:paragraph -->
+<p><strong>Inside</strong></p>
+<!-- /wp:paragraph -->"
+`;
+
 exports[`adding blocks should navigate around inline boundaries 1`] = `
 "<!-- wp:paragraph -->
 <p>FirstAfter</p>

test/e2e/specs/writing-flow.test.js

@@ -142,4 +142,22 @@ describe( 'adding blocks', () => {
 
 		expect( await getEditedPostContent() ).toMatchSnapshot();
 	} );
+
+	it( 'should clean TinyMCE content', async () => {
+		// Ensure no zero-width space character. Notably, this can occur when
+		// save occurs while at an inline boundary edge.
+		await page.click( '.editor-default-block-appender__content' );
+		await pressWithModifier( 'mod', 'b' );
+		expect( await getEditedPostContent() ).toMatchSnapshot();
+
+		// When returning to Visual mode, backspace in selected block should
+		// reset to the provisional block.
+		await page.keyboard.press( 'Backspace' );
+
+		// Ensure no data-mce-selected. Notably, this can occur when content
+		// is saved while typing within an inline boundary.
+		await pressWithModifier( 'mod', 'b' );
+		await page.keyboard.type( 'Inside' );
+		expect( await getEditedPostContent() ).toMatchSnapshot();
+	} );
 } );