Why isn't TypeScript giving an error?

type Unit = {
  unit: string;
  abbreviation: string;
  contains: string[];
};

const units: Unit[] = [{
  unit: "ounce",
  abbreviation: "oz",
  contains: ["ounce", "oz"]
}];

const getUnitAbbreviation = (ingredient: string) => {
  const filteredUnits = units.filter(({contains}) => contains.filter((cont) => ingredient.includes(cont)).length > 0)
  const sortedUnits = filteredUnits.sort((a, b) => b.unit.split(" ").length - a.unit.split(" ").length)
  const zeroth = sortedUnits[0];
  const abbv = zeroth.abbreviation;
  return abbv;
};

const shouldWork = getUnitAbbreviation("1 ounce of idk");
console.log("shouldWork", shouldWork);
const shouldFail = getUnitAbbreviation("1 idk of idk");
console.log("shouldFail", shouldFail);

type Unit = {
  unit: string;
  abbreviation: string;
  contains: string[];
};

const units: Unit[] = [{
  unit: "ounce",
  abbreviation: "oz",
  contains: ["ounce", "oz"]
}];

const getUnitAbbreviation = (ingredient: string) => {
  const filteredUnits = units.filter(({contains}) => contains.filter((cont) => ingredient.includes(cont)).length > 0)
  const sortedUnits = filteredUnits.sort((a, b) => b.unit.split(" ").length - a.unit.split(" ").length)
  const zeroth = sortedUnits[0];
  const abbv = zeroth.abbreviation;
  return abbv;
};

const shouldWork = getUnitAbbreviation("1 ounce of idk");
console.log("shouldWork", shouldWork);
const shouldFail = getUnitAbbreviation("1 idk of idk");
console.log("shouldFail", shouldFail);