This test verifies that setting an empty suggested value removes/resets the shadow placeholder value.

Input before setting suggested values:
| <input>
|   id="test"
|   type="text"
|   value="initial value"
|   this.value="initial value"
|   <shadow:root>
|     <div>
|       "initial value"
| <br>
| "
"
| <input>
|   id="inputwithplaceholder"
|   placeholder="initial placeholder"
|   type="text"
|   this.value=""
|   <shadow:root>
|     <div>
|       id="placeholder"
|       pseudo="-webkit-input-placeholder"
|       style="display: block !important; text-overflow: clip;"
|       shadow:pseudoId="-webkit-input-placeholder"
|       "initial placeholder"
|     <div>
| <br>
| "
"
| <textarea>
|   id="textarea"
|   this.value="initial value"
|   "initial value"
|   <shadow:root>
|     <div>
|       "initial value"
| <br>
| "
"
| <textarea>
|   id="textareaWithPlaceholder"
|   placeholder="initial placeholder"
|   this.value=""
|   <shadow:root>
|     <div>
|       id="placeholder"
|       pseudo="-webkit-input-placeholder"
|       style="display: block !important;"
|       shadow:pseudoId="-webkit-input-placeholder"
|       "initial placeholder"
|     <div>
| <br>
| "
"
| <select>
|   id="select"
|   <option>
|     "CA"
|     <shadow:root>
|       "CA"
|   <option>
|     "TX"
|     <shadow:root>
|       "TX"
|   <shadow:root>
|     <slot>
|       name="user-agent-custom-assign-slot"
| "input.value: initial value"
| "internals.suggestedValue(input): "
| "inputWithPlaceholder.value: "
| "internals.suggestedValue(inputWithPlaceholder): "
| "textarea.value: initial value"
| "internals.suggestedValue(textarea): "
| "textareaWithPlaceholder.value: "
| "internals.suggestedValue(textareaWithPlaceholder): "
| "select.value: "
| "internals.suggestedValue(select): "

Input after setting suggestedValue:
| <input>
|   id="test"
|   type="text"
|   value="initial value"
|   this.value="initial value"
|   <shadow:root>
|     <div>
|       id="placeholder"
|       pseudo="-internal-input-suggested"
|       style="display: block !important;"
|       shadow:pseudoId="-internal-input-suggested"
|       "suggested value"
|     <div>
|       "initial value"
| <br>
| "
"
| <input>
|   id="inputwithplaceholder"
|   placeholder="initial placeholder"
|   type="text"
|   this.value=""
|   <shadow:root>
|     <div>
|       id="placeholder"
|       pseudo="-internal-input-suggested"
|       style="display: block !important; text-overflow: clip;"
|       shadow:pseudoId="-internal-input-suggested"
|       "suggested value"
|     <div>
| <br>
| "
"
| <textarea>
|   id="textarea"
|   this.value="initial value"
|   "initial value"
|   <shadow:root>
|     <div>
|       id="placeholder"
|       pseudo="-internal-input-suggested"
|       style="display: block !important;"
|       shadow:pseudoId="-internal-input-suggested"
|       "suggested value"
|     <div>
|       "initial value"
| <br>
| "
"
| <textarea>
|   id="textareaWithPlaceholder"
|   placeholder="initial placeholder"
|   this.value=""
|   <shadow:root>
|     <div>
|       id="placeholder"
|       pseudo="-internal-input-suggested"
|       style="display: block !important;"
|       shadow:pseudoId="-internal-input-suggested"
|       "suggested value"
|     <div>
| <br>
| "
"
| <select>
|   id="select"
|   <option>
|     "CA"
|     <shadow:root>
|       "CA"
|   <option>
|     "TX"
|     <shadow:root>
|       "TX"
|   <shadow:root>
|     <slot>
|       name="user-agent-custom-assign-slot"
| "input.value: initial value"
| "internals.suggestedValue(input): "
| "inputWithPlaceholder.value: "
| "internals.suggestedValue(inputWithPlaceholder): "
| "textarea.value: initial value"
| "internals.suggestedValue(textarea): "
| "textareaWithPlaceholder.value: "
| "internals.suggestedValue(textareaWithPlaceholder): "
| "select.value: "
| "internals.suggestedValue(select): "
| "input.value: initial value"
| "internals.suggestedValue(input): suggested value"
| "inputWithPlaceholder.value: "
| "internals.suggestedValue(inputWithPlaceholder): suggested value"
| "textarea.value: initial value"
| "internals.suggestedValue(textarea): suggested value"
| "textareaWithPlaceholder.value: "
| "internals.suggestedValue(textareaWithPlaceholder): suggested value"
| "select.value: "
| "internals.suggestedValue(select): TX"

After resetting suggestedValue value:
| <input>
|   id="test"
|   type="text"
|   value="initial value"
|   this.value="initial value"
|   <shadow:root>
|     <div>
|       "initial value"
| <br>
| "
"
| <input>
|   id="inputwithplaceholder"
|   placeholder="initial placeholder"
|   type="text"
|   this.value=""
|   <shadow:root>
|     <div>
|       id="placeholder"
|       pseudo="-webkit-input-placeholder"
|       style="display: block !important; text-overflow: clip;"
|       shadow:pseudoId="-webkit-input-placeholder"
|       "initial placeholder"
|     <div>
| <br>
| "
"
| <textarea>
|   id="textarea"
|   this.value="initial value"
|   "initial value"
|   <shadow:root>
|     <div>
|       "initial value"
| <br>
| "
"
| <textarea>
|   id="textareaWithPlaceholder"
|   placeholder="initial placeholder"
|   this.value=""
|   <shadow:root>
|     <div>
|       id="placeholder"
|       pseudo="-webkit-input-placeholder"
|       style="display: block !important;"
|       shadow:pseudoId="-webkit-input-placeholder"
|       "initial placeholder"
|     <div>
| <br>
| "
"
| <select>
|   id="select"
|   <option>
|     "CA"
|     <shadow:root>
|       "CA"
|   <option>
|     "TX"
|     <shadow:root>
|       "TX"
|   <shadow:root>
|     <slot>
|       name="user-agent-custom-assign-slot"
| "input.value: initial value"
| "internals.suggestedValue(input): "
| "inputWithPlaceholder.value: "
| "internals.suggestedValue(inputWithPlaceholder): "
| "textarea.value: initial value"
| "internals.suggestedValue(textarea): "
| "textareaWithPlaceholder.value: "
| "internals.suggestedValue(textareaWithPlaceholder): "
| "select.value: "
| "internals.suggestedValue(select): "
| "input.value: initial value"
| "internals.suggestedValue(input): suggested value"
| "inputWithPlaceholder.value: "
| "internals.suggestedValue(inputWithPlaceholder): suggested value"
| "textarea.value: initial value"
| "internals.suggestedValue(textarea): suggested value"
| "textareaWithPlaceholder.value: "
| "internals.suggestedValue(textareaWithPlaceholder): suggested value"
| "select.value: "
| "internals.suggestedValue(select): TX"
| "input.value: initial value"
| "internals.suggestedValue(input): "
| "inputWithPlaceholder.value: "
| "internals.suggestedValue(inputWithPlaceholder): "
| "textarea.value: initial value"
| "internals.suggestedValue(textarea): "
| "textareaWithPlaceholder.value: "
| "internals.suggestedValue(textareaWithPlaceholder): "
| "select.value: "
| "internals.suggestedValue(select): "
| "PASS"