test: add unit test for p1

internal/2018/DayTwo/code_test.go

@@ -0,0 +1,21 @@
+package daytwo
+
+import "testing"
+
+var testInput = []string{
+	"abcdef",
+	"bababc",
+	"abbcde",
+	"abcccd",
+	"aabcdd",
+	"abcdee",
+	"ababab",
+}
+
+func TestPartOne(t *testing.T) {
+	expected := 12
+	got := PartOne(testInput)
+	if got != expected {
+		t.Errorf("PartOne() = %d, want %d", got, expected)
+	}
+}