Finished Testing Your Code, Refactoring for Testability

gradebook/src/GradeBook/Book.cs

@@ -3,6 +3,12 @@ using System.Collections.Generic;
 
 namespace GradeBook
 {
+    // public class Statistics
+    // {
+    //     public double Average;
+    //     public double highGrade;
+    //     public double lowGrade;
+    // }
     public class Book
     {
         private List<double> grades;
@@ -19,24 +25,22 @@ namespace GradeBook
             this.grades.Add(grade);
         }
 
-        public void ShowStaticstics()
+        public Statistics GetStatistics()
         {
+            var result = new Statistics();
+            result.Average = 0.0;
+            result.highGrade = double.MinValue;
+            result.lowGrade = double.MaxValue;
 
-            double result = 0;
-            var highGrade = double.MinValue;
-            var lowGrade = double.MaxValue;
-
-            foreach (var number in this.grades)
+            foreach (var grade in this.grades)
             {
-                highGrade = Math.Max(number, highGrade);
-                lowGrade = Math.Min(number, lowGrade);
-                result += number;
+                result.lowGrade = Math.Min(grade, result.lowGrade);
+                result.highGrade = Math.Max(grade, result.highGrade);
+                result.Average += grade;
             }
-            result /= grades.Count;
 
-            Console.WriteLine($"The average grade is {result:N1}");
-            Console.WriteLine($"The highest grade is {highGrade:N1}");
-            Console.WriteLine($"The lowest grade is {lowGrade:N1}");
+            result.Average /= grades.Count;
+            return result;
         }
     }
     

gradebook/src/GradeBook/Program.cs

@@ -12,7 +12,12 @@ namespace GradeBook
             book.AddGrade(89.1);
             book.AddGrade(90.5);
             book.AddGrade(87.2);
-            book.ShowStaticstics();
+            
+            var stats = book.GetStatistics();
+
+            Console.WriteLine($"The lowest grade is {stats.lowGrade}");
+            Console.WriteLine($"The highest grade is {stats.highGrade}");
+            Console.WriteLine($"The average grade is {stats.Average:N1}");
         }
     }
 }

gradebook/src/GradeBook/Statistics.cs

@@ -0,0 +1,9 @@
+namespace GradeBook
+{
+    public class Statistics
+    {
+        public double Average;
+        public double highGrade;
+        public double lowGrade;
+    }
+}

gradebook/test/GradeBook.Tests/BookTests.cs

@@ -16,7 +16,12 @@ namespace GradeBook.Tests
             book.AddGrade(77.3);
             
             // act
-            book.ShowStaticstics();
+            var result = book.GetStatistics();
+
+            // assert
+            Assert.Equal(85.6, result.Average, 1);
+            Assert.Equal(90.5, result.highGrade);
+            Assert.Equal(77.3, result.lowGrade);
         }
     }
 }