问为什么我的类型不满足约束？

EN

Type 'typeof TestBody' does not satisfy the constraint 'typeof AbstractBodyWithTabs'.
  Construct signature return types 'TestBody' and 'AbstractBodyWithTabs<T, U>' are incompatible.
    The types of 'contents' are incompatible between these types.
      Type 'TestContent' is not assignable to type 'T'.
        'TestContent' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint 'AbstractSelector'.

class TestPage extends PageWithTabs<typeof TestBody> {

export class AbstractSelector {
    protected readonly myRoot : Selector
    
    constructor(inSelector : Selector) {
        this.myRoot = inSelector;
    }
}
export abstract class AbstractBodyWithTabs<
    T extends AbstractSelector, 
    U extends Tabs
> {
    abstract get contents () : T
    abstract get tabs () : U
    get wrapper () : Selector {
        return Selector(".app-component");
    }
}
export abstract class Tabs extends AbstractSelector {
    get active () {
        return this.wrapper.find(":scope > button[contains(@class, 'focus')]");
    }
    get all () {
        return this.wrapper.find(":scope > button");
    }
    abstract get named_tab () : Record<string, Selector>;
    get wrapper () {
        return this.myRoot.find("div.btn-group");
    }
}
export abstract class PageWithTabs<V extends typeof AbstractBodyWithTabs> {
    abstract get body () : InstanceType<V>
    get footer () {
        return new SaveAndCancelFooter();
    }
    get header () {
        return new Header();
    }
}

class TestContent extends AbstractSelector {

}
class TestTabs extends Tabs {
    get named_tab () {
        return { get country () { return Selector("div"); } };
    }
}
class TestBody extends AbstractBodyWithTabs<TestContent, TestTabs> {
    get contents () {
        return new TestContent(this.wrapper);
    }
    get tabs () {
        return new TestTabs(this.wrapper);
    }
}
class TestPage extends PageWithTabs<typeof TestBody> {
    get body () {
        return new TestBody();
    }
}

export abstract class PageWithTabs<V extends typeof AbstractBodyWithTabs> {
    abstract get body () : InstanceType<V>
    get footer () {
        return new SaveAndCancelFooter();
    }
    get header () {
        return new Header();
    }
}

export abstract class PageWithTabs<T extends AbstractSelector, U extends Tabs, V extends AbstractBodyWithTabs<T, U>> {
    abstract get body () : V
    get footer () {
        return new SaveAndCancelFooter();
    }
    get header () {
        return new Header();
    }
}

class TestPage extends PageWithTabs<typeof TestBody> {
    get body () {
        return new TestBody();
    }
}

class TestPage extends PageWithTabs<TestContent, TestTabs, TestBody> {
    get body () {
        return new TestBody();
    }
}