Always propagate root context to child command

The context passed to the root command should propagate to its children
not only on the first execution but also subsequent calls.
Calling the same command multiple times is common when testing cobra applications.

command.go

@@ -1059,11 +1059,8 @@ func (c *Command) ExecuteC() (cmd *Command, err error) {
 		cmd.commandCalledAs.name = cmd.Name()
 	}
 
-	// We have to pass global context to children command
-	// if context is present on the parent command.
-	if cmd.ctx == nil {
-		cmd.ctx = c.ctx
-	}
+	// Pass context of root command to child command.
+	cmd.ctx = c.ctx
 
 	err = cmd.execute(flags)
 	if err != nil {

command_test.go

@@ -232,6 +232,44 @@ func TestExecuteContextC(t *testing.T) {
 	}
 }
 
+// This tests that the context passed to the root command propagates to its children
+// not only on the first execution but also subsequent calls.
+// Calling the same command multiple times is common when testing cobra applications.
+func TestExecuteContextMultipleTimes(t *testing.T) {
+	ctxRun := func(cmd *Command, args []string) {
+		err := cmd.Context().Err()
+		if err != nil {
+			t.Errorf("Context of command %q has error: %s", cmd.Use, err)
+		}
+	}
+
+	rootCmd := &Command{Use: "root", Run: ctxRun, PreRun: ctxRun}
+	childCmd := &Command{Use: "child", Run: ctxRun, PreRun: ctxRun}
+	granchildCmd := &Command{Use: "grandchild", Run: ctxRun, PreRun: ctxRun}
+
+	childCmd.AddCommand(granchildCmd)
+	rootCmd.AddCommand(childCmd)
+
+	for i := 0; i < 2; i++ {
+		ctx, cancel := context.WithCancel(context.Background())
+
+		if _, err := executeCommandWithContext(ctx, rootCmd, ""); err != nil {
+			t.Errorf("Root command must not fail: %+v", err)
+		}
+
+		if _, err := executeCommandWithContext(ctx, rootCmd, "child"); err != nil {
+			t.Errorf("Subcommand must not fail: %+v", err)
+		}
+
+		if _, err := executeCommandWithContext(ctx, rootCmd, "child", "grandchild"); err != nil {
+			t.Errorf("Command child must not fail: %+v", err)
+		}
+
+		// Invalidate the context of this iteration.
+		cancel()
+	}
+}
+
 func TestExecute_NoContext(t *testing.T) {
 	run := func(cmd *Command, args []string) {
 		if cmd.Context() != context.Background() {