The description for field ExpectedHttpStatusCode is incomplete. When creating a Web Test via the Azure portal, there is an option to select "<400" for the ExpectedHttpStatusCode property, and the property description does not include information on how to leverage that setting (the property is of type Integer). It appears that ommitting ExpectedHttpStatusCode from the parameters, or setting it to zero, is the way to configure that setting to "<400", via Bicep. The documentation does not mention this.