(Medium) - How TDD Can Prevent Over-Engineering

StoreRangeInLiteral.diff

   }
 
   const calculateInterestForGreaterThan2000 = (loanAmount, endOfRange, interestPerDollar, previousInterestPerDollar) => {
-    const dollarsAboveThreshold = loanAmount.minus(endOfRange);
-    const interestToPay = interestPerDollar.minus(previousInterestPerDollar).multipliedBy(dollarsAboveThreshold);
+    const greaterThan2000 = {
+      endOfRange: endOfRange,
+      interestPerDollar: interestPerDollar,
+      previousInterestPerDollar: previousInterestPerDollar
+    };
+    const dollarsAboveThreshold = loanAmount.minus(greaterThan2000.endOfRange);
+    const interestToPay = greaterThan2000.interestPerDollar.minus(greaterThan2000.previousInterestPerDollar).multipliedBy(dollarsAboveThreshold);
     return interestToPay;
   };