Move up Example.Tests a level

Example.Tests/Calculator.fs

@@ -0,0 +1,10 @@
+namespace Example
+
+module Calculator =
+    let addOne value = value + 1
+
+    let absoluteDifference left right =
+        if left >= right then left - right else right - left
+
+    let isLeapYear year =
+        year % 4 = 0 && (year % 100 <> 0 || year % 400 = 0)