Add CreatedAtTimestamp and fix CreatedAt docs

Signed-off-by: Simon H <simon9ha@gmail.com>

cli/command/formatter/container.go

@@ -192,11 +192,16 @@ func (c *ContainerContext) Command() string {
 	return strconv.Quote(command)
 }
 
-// CreatedAt returns the "Created" date/time of the container as a unix timestamp.
+// CreatedAt returns the "Created" date/time of the container as a string
 func (c *ContainerContext) CreatedAt() string {
 	return time.Unix(c.c.Created, 0).String()
 }
 
+// CreatedAtTimestamp returns the "Created" date/time of the container as a unix timestamp
+func (c *ContainerContext) CreatedAtTimestamp() time.Time {
+	return time.Unix(c.c.Created, 0)
+}
+
 // RunningFor returns a human-readable representation of the duration for which
 // the container has been running.
 //

cli/command/formatter/container_test.go

@@ -336,16 +336,19 @@ func TestContainerContextWriteWithNoContainers(t *testing.T) {
 }
 
 func TestContainerContextWriteJSON(t *testing.T) {
-	unix := time.Now().Add(-65 * time.Second).Unix()
+	ts := time.Now().Add(-65 * time.Second)
+	unix := ts.Unix()
 	containers := []types.Container{
 		{ID: "containerID1", Names: []string{"/foobar_baz"}, Image: "ubuntu", Created: unix, State: "running"},
 		{ID: "containerID2", Names: []string{"/foobar_bar"}, Image: "ubuntu", Created: unix, State: "running"},
 	}
 	expectedCreated := time.Unix(unix, 0).String()
+	expectedCreatedAtTimestamp := ts.Format(time.RFC3339)
 	expectedJSONs := []map[string]any{
 		{
 			"Command":            "\"\"",
 			"CreatedAt":          expectedCreated,
+			"CreatedAtTimestamp": expectedCreatedAtTimestamp,
 			"ID":                 "containerID1",
 			"Image":              "ubuntu",
 			"Labels":             "",
@@ -362,6 +365,7 @@ func TestContainerContextWriteJSON(t *testing.T) {
 		{
 			"Command":            "\"\"",
 			"CreatedAt":          expectedCreated,
+			"CreatedAtTimestamp": expectedCreatedAtTimestamp,
 			"ID":                 "containerID2",
 			"Image":              "ubuntu",
 			"Labels":             "",