This is a testharness.js-based test.
PASS Navigator interface: attribute mediaCapabilities 
PASS Navigator must be primary interface of navigator 
PASS Stringification of navigator 
PASS Navigator interface: navigator must inherit property "mediaCapabilities" with the proper type (0) 
PASS WorkerNavigator interface: existence and properties of interface object 
PASS MediaCapabilitiesInfo interface: existence and properties of interface object 
PASS MediaCapabilitiesInfo interface object length 
PASS MediaCapabilitiesInfo interface object name 
FAIL MediaCapabilitiesInfo interface: existence and properties of interface prototype object assert_equals: class string of MediaCapabilitiesInfo.prototype expected "[object MediaCapabilitiesInfoPrototype]" but got "[object MediaCapabilitiesInfo]"
PASS MediaCapabilitiesInfo interface: existence and properties of interface prototype object's "constructor" property 
PASS MediaCapabilitiesInfo interface: attribute supported 
PASS MediaCapabilitiesInfo interface: attribute smooth 
PASS MediaCapabilitiesInfo interface: attribute powerEfficient 
PASS MediaCapabilities interface: existence and properties of interface object 
PASS MediaCapabilities interface object length 
PASS MediaCapabilities interface object name 
FAIL MediaCapabilities interface: existence and properties of interface prototype object assert_equals: class string of MediaCapabilities.prototype expected "[object MediaCapabilitiesPrototype]" but got "[object MediaCapabilities]"
PASS MediaCapabilities interface: existence and properties of interface prototype object's "constructor" property 
FAIL MediaCapabilities interface: operation decodingInfo(MediaDecodingConfiguration) assert_throws: calling operation with this = null didn't throw TypeError function "function () {
            fn.apply(obj, args);
        }" did not throw
FAIL MediaCapabilities interface: operation encodingInfo(MediaEncodingConfiguration) assert_own_property: interface prototype object missing non-static operation expected property "encodingInfo" missing
Harness: the test ran to completion.