foo.spec.ts

describe('Foo Class', () => {
  describe('constructor', () => {
    const fooClassRef = Foo as any; // to pass typechecking
    
    beforeEach(() => {
      console.log(`start of beforeEach: ${fooClassRef._count}`);
      fooClassRef._count = 0;
      console.log(`end of beforeEach: ${fooClassRef._count}`);
    });
    
    describe('creating one Foo obj', () => {
      console.log(fooClassRef._count);
      const foo = new Foo();
      
      it('should have an id of 1', () => {
        expect(foo.id).toBe(1);
      });
    });
    
    describe('creating two Foo objs', () => {
      console.log(fooClassRef._count);
      const foo1 = new Foo();
      const foo2 = new Foo();
    
      it('should have ids of 1 and 2', () => {
        expect(foo1.id).toBe(1);
        expect(foo2.id).toBe(2);
      });
    });
  });
});

A little white space goes a long way. At least, it makes it clearer to me where you went wrong. It took a moment to notice.

describe('Foo Class', () => {
  describe('constructor', () => {
    const fooClassRef = Foo as any; // to pass typechecking

    beforeEach(() => {
      console.log(`start of beforeEach: ${fooClassRef._count}`);
      fooClassRef._count = 0;
      console.log(`end of beforeEach: ${fooClassRef._count}`);
    });

    describe('creating one Foo obj', () => {
      console.log(fooClassRef._count);
      const foo = new Foo();

      it('should have an id of 1', () => {
        expect(foo.id).toBe(1);
      });
    });

    describe('creating two Foo objs', () => {
      console.log(fooClassRef._count);
      const foo1 = new Foo();
      const foo2 = new Foo();

      it('should have ids of 1 and 2', () => {
        expect(foo1.id).toBe(1);
        expect(foo2.id).toBe(2);
      });
    });
  });
});

👍

Updated. Ty!