test: add unit tests for P1/P2

internal/2018/DayOne/code_test.go

@@ -0,0 +1,26 @@
+package dayone
+
+import "testing"
+
+var testInput = []int{
+	+1,
+	-2,
+	3,
+	1,
+}
+
+func TestPartOne(t *testing.T) {
+	expected := 3
+	got := PartOne(testInput)
+	if got != expected {
+		t.Errorf("PartOne() = %d, want %d", got, expected)
+	}
+}
+
+func TestPartTwo(t *testing.T) {
+	expected := 2
+	got := PartTwo(testInput)
+	if got != expected {
+		t.Errorf("PartTwo() = %d, want %d", got, expected)
+	}
+}