How to access javascript object props with dynamic col names

Trying access a deep object props with a predefined variable name.I see the result as undefined. Can someone please suggest best way to handle it

const testObject = {
      a :{
        b: {
          c: 'hello'
        }
      }
    }
    
    const testCol = "a.b.c"
    
    console.log(testObject.testCol)