String Literal Type does not work #20271

// A *self-contained* demonstration of the problem follows...
// Test this by running `tsc` on the command-line, rather than through another build tool such as Gulp, Webpack, etc.
interface TypeA {
    test: "test1" | "test2" | "test3"
}

function fn(param: TypeA) {

}

// Check pass
fn({
    test: "test1"
});

// The same object, but passed by object reference
let obj = {
    test: "test1"
};

/**
 * Error:(26, 4) TS2345: Argument of type '{ test: string; }' is not assignable to parameter of type 'TypeA'.
 *   Types of property 'test' are incompatible.
 *   Type 'string' is not assignable to type '"test1" | "test2" | "test3"'.
 */
fn(obj);