Add format-time exercise

This follows on from the prep.

Author: illicitonion

Sprint-2/extend/format-time.js

@@ -0,0 +1,24 @@
+// This is the latest solution to the problem from the prep.
+// Your task is to write tests for as many different groups of input data or edge cases as you can, and fix any bugs you find.
+
+function formatAs12HourClock(time) {
+  const hours = Number(time.slice(0, 2));
+  if (hours > 12) {
+    return `${hours - 12}:00 pm`;
+  }
+  return `${time} am`;
+}
+
+const currentOutput = formatAs12HourClock("08:00");
+const targetOutput = "08:00 am";
+console.assert(
+  currentOutput === targetOutput,
+  `current output: ${currentOutput}, target output: ${targetOutput}`
+);
+
+const currentOutput2 = formatAs12HourClock("23:00");
+const targetOutput2 = "11:00 pm";
+console.assert(
+  currentOutput2 === targetOutput2,
+  `current output: ${currentOutput2}, target output: ${targetOutput2}`
+);

Sprint-2/readme.md

@@ -23,3 +23,8 @@ Here is a recommended order:
 In these tasks, you have to interpret a slightly larger program with some syntax / operators / functions that may be unfamiliar.
 You must use documentation to make sense of anything unfamiliar - learning how to look things up this way is a fundamental part of being a developer!
 You can also use `console.log` to check the value of different variables in the code.
+
+## Extend
+
+In the prep for this sprint, we developed a function to convert 24 hour clock times to 12 hour clock times.
+Your task is to write tests for as many different groups of input data or edge cases as you can, and fix any bugs you find.