From 77a1027ab037c254d2586935cffeb720fe1daba4 Mon Sep 17 00:00:00 2001
From: Drew Bednar <drew@runcible.io>
Date: Sun, 13 Oct 2024 18:43:30 -0400
Subject: [PATCH] Failing concurrent test

---
 learn_go_with_tests/my_sync/go.mod          |  3 ++
 learn_go_with_tests/my_sync/my_sync.go      | 13 ++++++
 learn_go_with_tests/my_sync/my_sync_test.go | 44 +++++++++++++++++++++
 3 files changed, 60 insertions(+)
 create mode 100644 learn_go_with_tests/my_sync/go.mod
 create mode 100644 learn_go_with_tests/my_sync/my_sync.go
 create mode 100644 learn_go_with_tests/my_sync/my_sync_test.go

diff --git a/learn_go_with_tests/my_sync/go.mod b/learn_go_with_tests/my_sync/go.mod
new file mode 100644
index 0000000..e52cb81
--- /dev/null
+++ b/learn_go_with_tests/my_sync/go.mod
@@ -0,0 +1,3 @@
+module my_sync
+
+go 1.23.1
diff --git a/learn_go_with_tests/my_sync/my_sync.go b/learn_go_with_tests/my_sync/my_sync.go
new file mode 100644
index 0000000..d56aca6
--- /dev/null
+++ b/learn_go_with_tests/my_sync/my_sync.go
@@ -0,0 +1,13 @@
+package my_sync
+
+type Counter struct {
+	count int
+}
+
+func (c *Counter) Inc() {
+	c.count++
+}
+
+func (c *Counter) Value() int {
+	return c.count
+}
diff --git a/learn_go_with_tests/my_sync/my_sync_test.go b/learn_go_with_tests/my_sync/my_sync_test.go
new file mode 100644
index 0000000..f544c74
--- /dev/null
+++ b/learn_go_with_tests/my_sync/my_sync_test.go
@@ -0,0 +1,44 @@
+package my_sync
+
+import (
+	"sync"
+	"testing"
+)
+
+func assertCount(t testing.TB, got Counter, want int) {
+	t.Helper()
+	if got.Value() != want {
+		t.Errorf("got %d, want %d", got.Value(), want)
+	}
+}
+
+func TestCounter(t *testing.T) {
+	t.Run("Incrementing the counter 3 times leaves it at 3", func(t *testing.T) {
+		counter := Counter{}
+		counter.Inc()
+		counter.Inc()
+		counter.Inc()
+
+		assertCount(t, counter, 3)
+
+	})
+
+	t.Run("it runs safely concurrently", func(t *testing.T) {
+		wantedCount := 1000
+		counter := Counter{}
+
+		var wg sync.WaitGroup
+		wg.Add(wantedCount)
+
+		for i := 0; i < wantedCount; i++ {
+			go func() {
+				counter.Inc()
+				wg.Done()
+			}()
+		}
+		// blocking call to wait for all goroutines
+		wg.Wait()
+
+		assertCount(t, counter, wantedCount)
+	})
+}