Add tests for fibonacci series

Test Driven Development in Ruby/fibonacci sequece/fibonacci.rb

@@ -0,0 +1,7 @@
+class Fibonacci
+  def self.of(n)
+    return 0 if n == 0
+    return 1 if n <= 2
+    return of(n - 1) + of(n - 2)
+  end
+end

Test Driven Development in Ruby/fibonacci sequece/test_fibonacci.rb

@@ -0,0 +1,29 @@
+require 'minitest/autorun'
+require_relative 'fibonacci'
+
+class TestFibonacci < Minitest::Test
+  def test_fibonacci_of_zero_is_zero
+    result = Fibonacci.of(0)
+    assert_equal 0, result
+  end
+
+  def test_fibonacci_of_one_is_one
+    result = Fibonacci.of(1)
+    assert_equal 1, result
+  end
+
+  def test_fibonacci_of_two_is_one
+    result = Fibonacci.of(2)
+    assert_equal 1, result
+  end
+
+  def test_fibonacci_of_three_is_two
+    result = Fibonacci.of(3)
+    assert_equal 2, result
+  end
+
+  def test_fibonacci_of_ten_is_fifty_five
+    result = Fibonacci.of(10)
+    assert_equal 55, result
+  end
+end