feat: One more concurrency exercise

exercises/concurrent/concurrent3/main_test.go

@@ -0,0 +1,43 @@
+// concurrent3
+// Make the tests pass!
+
+// I AM NOT DONE
+package main_test
+
+import (
+	"bytes"
+	"fmt"
+	"testing"
+)
+
+func TestSendAndReceive(t *testing.T) {
+	var buf bytes.Buffer
+
+	messages := make(chan string)
+	sendAndReceive(&buf, messages)
+
+	got := buf.String()
+	want := "Hello World"
+
+	if got != want {
+		t.Errorf("got %q want %q", got, want)
+	}
+}
+
+func sendAndReceive(buf *bytes.Buffer, messages chan string) {
+	go func() {
+		messages <- "Hello"
+		messages <- "World"
+		close(messages)
+	}()
+
+	greeting := <-messages
+	fmt.Fprint(buf, greeting)
+
+	// Here we just receive the first message
+	// Consider using a for-range loop to iterate over the messages
+	_, ok := <-messages
+	if !ok {
+		fmt.Fprint(buf, "Channel is closed")
+	}
+}

info.toml

@@ -342,3 +342,15 @@ A counter is a good example. Your counter could be updated with a different valu
 
 Read a little about mutexes: https://pkg.go.dev/sync#Mutex.
 """
+
+[[exercises]]
+name = "concurrent3"
+path = "exercises/concurrent/concurrent3/main_test.go"
+mode = "test"
+hint = """
+Writing messages to closed channels will panic.
+
+To avoid panics, we don't want to send messages to closed channels.
+
+Remember: channels can be iterated using for-range loops.
+"""