✨ (sum_test): add test first

Author: yuanyu90221

.gitignore

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+# If you prefer the allow list template instead of the deny list, see community template:
+# https://github.com/github/gitignore/blob/main/community/Golang/Go.AllowList.gitignore
+#
+# Binaries for programs and plugins
+*.exe
+*.exe~
+*.dll
+*.so
+*.dylib
+
+# Test binary, built with `go test -c`
+*.test
+
+# Output of the go coverage tool, specifically when used with LiteIDE
+*.out
+
+# Dependency directories (remove the comment below to include it)
+# vendor/
+
+# Go workspace file
+go.work
+go.work.sum
+
+# env file
+.env
+bin

Makefile

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+.PHONY=build
+# include .env
+# export $(shell sed 's/=.*//' .env)
+
+coverage:
+	@go test -v -cover ./...
+
+test:
+	@go test -v ./...

README.md

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+
+# Arrays 與 Slices
+
+在 golang 中，陣列類型資料類型主要有兩種 array 與 slice 。
+
+## array
+array 是一種固定長度的資料陣列。在初始化時，就設定好長度，並且無法後續修改。
+
+```golang=
+arr := [4]int{1,1,1,1}
+arr := [...]int{1,1,1,1}
+```
+
+![image](https://hackmd.io/_uploads/HkY6BHIbex.png)
+
+## slice
+
+slice 是則是一種動態長度的資料陣列。在初始化，可以設定好容量 capacity 。可以透過 append 新增資料到 slice 上。而實際上， slice 內部是指向一個 array 資料型態的參考，遇到超過預設 capacity 的資料量時，就會產生新的二倍於原本 capacity 的陣列實體，然後把 slice 參考更新。
+
+```golang=
+slice := []int{1,1,1,1}
+// slice 的預設的 capcity 會是當下資料量長度，當不指定時
+// slice 基本有3個屬性 ptr 指向目前資料陣列參照， len 代表當下資料長度， cap 代表當下最多容量。
+```
+
+![image](https://hackmd.io/_uploads/rJixLSI-xg.png)
+
+# iteration
+
+```golang=
+stockAmountByDay := []int{200,210, 300,311}
+```
+## loop over by index
+
+```golang=
+sliceLength := len(stockAmountByDay)
+for idx := 0; idx < sliceLength; idx++ {
+   stockAmount := stockAmountByDay[idx]
+   fmt.Printf("stockAmount = %d\n",stockAmount)
+}  
+```
+[iteration-slice-by-idx](https://go.dev/play/p/w_iYwtB6u6c)
+
+## loop over by range
+
+```golang=
+for _, stockAmount := range stockAmountByDay {
+   fmt.Printf("stockAmount = %d\n",stockAmount)
+}
+```
+
+[iteration-slice-by-range](https://go.dev/play/p/CYLQDp2p4mY)
+
+# operation
+
+## append
+
+```golang=
+stockAmountByDay = append(stockAmountByDay, 170)
+```
+![image](https://hackmd.io/_uploads/S1pQsT8-xl.png)
+[append-example](https://go.dev/play/p/843TDDp3N6I)
+
+## sub range reference
+```golang=
+stockAmountByDayRange := stockAmountByDay[1:4]
+```
+
+![image](https://hackmd.io/_uploads/rJow3a8Wge.png)
+[sub-range-reference](https://go.dev/play/p/K9x8MOBA3gh)
+
+
+## copy
+```golang=
+stockAmountByRangeClone := make([]int, len(stockAmountByRange))
+copy(stockAmountByRangeClone, stockAmountByRange)
+```
+
+![image](https://hackmd.io/_uploads/rkGH8C8Zge.png)
+
+[copy-example](https://go.dev/play/p/4v2qE0jikrb)
+
+
+# 參考文件
+
+[slice-intro](https://go.dev/blog/slices-intro)

arrays-and-slices/sum_test.go

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+package arrays_and_slices
+
+import "testing"
+
+func TestSum(t *testing.T) {
+	numbers := [5]int{1, 2, 3, 4, 5}
+
+	got := Sum(numbers)
+	want := 15
+
+	if got != want {
+		t.Errorf("got %d want %d ,given %v", got, want, numbers)
+	}
+}

go.mod

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+module github.com/leetcode-golang-classroom/learn-golang-with-tests
+
+go 1.24.0