Angular Jasmine FormControl Unit Test valueChanges

I want to unit test my following method:

this.boxValue = '';

subscribeToFilterChanges(): void {
this.filterBox.valueChanges
.subscribe(
data => {
if (data) {
this.boxValue = data.trim().toLowerCase();
}
}
);
}


filterBox is a FormControl:

filterBox = new FormControl('');


HTML is:

<mat-form-field appearance="standard">
<input matInput [formControl]="filterBox"
id="filterBox-input">
</mat-form-field>


I've written the unit test as:

it('verify filter changes', () => {
let filterBoxInput = fixture.debugElement.query(By.css('#filterBox-input'));
filterBoxInput.nativeElement.value = 'dummy';
filterBoxInput.nativeElement.dispatchEvent(new Event('input'));
fixture.detectChanges();
fixture.whenStable().then(() => {
expect(component.boxValue).toBe('dummy1');
});
});


This test should fail, but still it is showing as passed, even though incorrect value is specified in .toBe()

What could be the issue?

I referred to Angular Testing: FormControl valueChanges Observable

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