Add package description and unit test

internal/slice/slice.go

@@ -1,8 +1,9 @@
+// Package slice defines functions to manipulate the slice
 package slice
 
 import "reflect"
 
-// Contains return whether list has elem.
+// Contains returns whether the list has the elements specified in the argument.
 func Contains(list interface{}, elem interface{}) bool {
 	rvList := reflect.ValueOf(list)
 

internal/slice/slice_test.go

@@ -0,0 +1,71 @@
+package slice
+
+import "testing"
+
+func TestContains(t *testing.T) {
+	type args struct {
+		list interface{}
+		elem interface{}
+	}
+	tests := []struct {
+		name string
+		args args
+		want bool
+	}{
+		{
+			name: "[Success] string slice has 'metallica'",
+			args: args{
+				list: []string{"a", "bb", "metallica", "abc"},
+				elem: "metallica",
+			},
+			want: true,
+		},
+		{
+			name: "[Success] string slice does not have 'metallica'",
+			args: args{
+				list: []string{"a", "bbb", "abc"},
+				elem: "metallica",
+			},
+			want: false,
+		},
+		{
+			name: "[Success] Integer slice has 100",
+			args: args{
+				list: []int64{1, 3, 100, 21},
+				elem: 100,
+			},
+			want: true,
+		},
+		{
+			name: "[Success] Integer slice  does not have 100",
+			args: args{
+				list: []int64{1, 3, 21},
+				elem: 100,
+			},
+			want: false,
+		},
+		{
+			name: "[Error] If the slice and element types are different",
+			args: args{
+				list: []string{"a", "bb", "metallica", "abc"},
+				elem: -100,
+			},
+			want: false,
+		},
+		{
+			name: "[Error] If both arguments are slices",
+			args: args{
+				list: []string{"a", "bb", "metallica", "abc"},
+				elem: []int64{1, 3, 21},
+			},
+			want: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := Contains(tt.args.list, tt.args.elem); got != tt.want {
+				t.Errorf("Contains() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}