Update documentaiton on interactions with context.

README.md

@@ -36,6 +36,7 @@ Now you can easily test `myFunc` with a `FakeClock`:
 
 ```go
 func TestMyFunc(t *testing.T) {
+	ctx := context.Background()
 	c := clockwork.NewFakeClock()
 
 	// Start our sleepy function
@@ -46,8 +47,12 @@ func TestMyFunc(t *testing.T) {
 		wg.Done()
 	}()
 
-	// Ensure we wait until myFunc is sleeping
-	c.BlockUntil(1)
+	// Ensure we wait until myFunc is waiting on the clock.
+	// Use a context to avoid blocking forever if something
+	// goes wrong.
+	ctx, cancel := context.WithTimeout(ctx, 10*time.Second)
+	defer cancel()
+	c.BlockUntilContext(ctx, 1)
 
 	assertState()
 

context.go

@@ -4,14 +4,16 @@ import (
 	"context"
 )
 
-// contextKey is private to this package, so we can ensure uniqueness here. This
+// contextKey is private to this package so we can ensure uniqueness here. This
 // type identifies context values provided by this package.
 type contextKey string
 
-// keyClock provides a clock for injecting during tests. If absent, a real clock should be used.
-var keyClock = contextKey("clock") // clockwork.Clock
-
 // AddToContext creates a derived context that references the specified clock.
+//
+// Be aware this doesn't change the behavior of standard library functions, such
+// as [context.WithTimeout] or [context.WithDeadline]. For this reason, users
+// should prefer passing explicit [clockwork.Clock] variables rather can passing
+// the clock via the context.
 func AddToContext(ctx context.Context, clock Clock) context.Context {
 	return context.WithValue(ctx, keyClock, clock)
 }

example_test.go

@@ -1,6 +1,7 @@
 package clockwork
 
 import (
+	"context"
 	"sync"
 	"testing"
 	"time"
@@ -21,6 +22,7 @@ func assertState(t *testing.T, i, j int) {
 
 // TestMyFunc tests myFunc's behaviour with a FakeClock.
 func TestMyFunc(t *testing.T) {
+	ctx := context.Background()
 	var i int
 	c := NewFakeClock()
 
@@ -31,8 +33,12 @@ func TestMyFunc(t *testing.T) {
 		wg.Done()
 	}()
 
-	// Wait until myFunc is actually sleeping on the clock.
-	c.BlockUntil(1)
+	// Ensure we wait until myFunc is waiting on the clock.
+	// Use a context to avoid blocking forever if something
+	// goes wrong.
+	ctx, cancel := context.WithTimeout(ctx, 10*time.Second)
+	defer cancel()
+	c.BlockUntilContext(ctx, 1)
 
 	// Assert the initial state.
 	assertState(t, i, 0)