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//! Scenarios
//!
//! In general you will not need to interact with the [`Scenario`] type directly.
//! Instead instances of it are constructed in the generated test functions and
//! will be run automatically.
use std::{cell::RefCell, marker::PhantomData, sync::Mutex};
use state::Container;
use crate::step::ScenarioStep;
use crate::types::{StepError, StepResult};
/// A context element is anything which can be used as a scenario step context.
///
/// Contexts get called whenever the scenario steps occur so that they can do
/// prep, cleanup, etc. It's important for authors of context element types to
/// be aware that they won't always be called on scenario start and they will
/// not be caught up the first time they are invoked for a step, simply expected
/// to get on with life from their first use.
pub trait ContextElement: Default + Send + 'static {
/// A new context element was created.
///
/// In order to permit elements which for example work on disk, this
/// function will be invoked with the scenario's context to permit the
/// context to register other contexts it might need, or to permit the
/// creation of suitably named temporary directories, logging, etc.
///
/// The scenario's title is available via [`scenario_context.title()`][title]
///
/// [title]: [ScenarioContext::title]
#[allow(unused_variables)]
fn created(&mut self, scenario: &Scenario) {
// Nothing by default
}
/// Scenario starts
///
/// When a scenario starts, this function is called to permit setup.
///
/// If this returns an error, scenario setup is stopped and `scenario_stops`
/// will be called for anything which succeeded at startup.
fn scenario_starts(&mut self) -> StepResult {
Ok(())
}
/// Scenario stops
///
/// When a scenario finishes, this function is called to permit teardown.
///
/// If this returns an error, and the scenario would otherwise have passed,
/// then the error will be used. The first encountered error in stopping
/// a scenario will be used, rather than the last. All contexts which
/// succeeded at starting will be stopped.
fn scenario_stops(&mut self) -> StepResult {
Ok(())
}
/// Entry to a step function
///
/// In order to permit elements which for example work on disk, this
/// function will be invoked with the step's name to permit the creation of
/// suitably named temporary directories, logging, etc.
///
/// The default implementation of this does nothing.
///
/// Calls to this function *will* be paired with calls to the step exit
/// function providing nothing panics or calls exit without unwinding.
///
/// If you wish to be resilient to step functions panicing then you will
/// need to be careful to cope with a new step being entered without a
/// previous step exiting. Particularly if you're handing during cleanup
/// of a failed scenario.
///
/// If this returns an error then the step function is not run, nor is the
/// corresponding `exit_step()` called.
#[allow(unused_variables)]
fn step_starts(&mut self, step_title: &str) -> StepResult {
Ok(())
}
/// Exit from a step function
///
/// See [the `step_starts` function][ContextElement::step_starts] for most
/// details of this.
///
/// Any error returned from this will be masked if the step function itself
/// returned an error. However if the step function succeeded then this
/// function's error will make it out.
#[allow(unused_variables)]
fn step_stops(&mut self) -> StepResult {
Ok(())
}
}
/// A scenario context wrapper for a particular context type
struct ScenarioContextItem<C>(Mutex<C>);
/// A type hook used purely in order to be able to look up contexts in the
/// container in order to be able to iterate them during scenario execution
struct ScenarioContextHook<C>(PhantomData<C>);
impl<C> ScenarioContextHook<C>
where
C: ContextElement,
{
fn new() -> Self {
Self(PhantomData::default())
}
}
/// A trait used to permit the holding of multiple hooks in one vector
trait ScenarioContextHookKind {
/// Start scenario
fn scenario_starts(&self, contexts: &ScenarioContext) -> StepResult;
/// Stop scenario
fn scenario_stops(&self, contexts: &ScenarioContext) -> StepResult;
/// Enter a step
fn step_starts(&self, contexts: &ScenarioContext, step_name: &str) -> StepResult;
/// Leave a step
fn step_stops(&self, contexts: &ScenarioContext) -> StepResult;
}
impl<C> ScenarioContextHookKind for ScenarioContextHook<C>
where
C: ContextElement,
{
fn scenario_starts(&self, contexts: &ScenarioContext) -> StepResult {
contexts.with_mut(|c: &mut C| c.scenario_starts(), false)
}
fn scenario_stops(&self, contexts: &ScenarioContext) -> StepResult {
contexts.with_mut(|c: &mut C| c.scenario_stops(), true)
}
fn step_starts(&self, contexts: &ScenarioContext, step_name: &str) -> StepResult {
contexts.with_mut(|c: &mut C| c.step_starts(step_name), false)
}
fn step_stops(&self, contexts: &ScenarioContext) -> StepResult {
contexts.with_mut(|c: &mut C| c.step_stops(), true)
}
}
/// A container for all scenario contexts
///
/// This container allows the running of code within a given scenario context.
pub struct ScenarioContext {
title: String,
inner: Container![],
hooks: RefCell<Vec<Box<dyn ScenarioContextHookKind>>>,
}
impl ScenarioContext {
fn new(title: &str) -> Self {
Self {
title: title.to_string(),
inner: <Container![]>::new(),
hooks: RefCell::new(Vec::new()),
}
}
/// The title for this scenario
fn title(&self) -> &str {
&self.title
}
/// Ensure a context is registered
pub(crate) fn register_context_type<C>(&self) -> bool
where
C: ContextElement,
{
let sci: Option<&ScenarioContextItem<C>> = self.inner.try_get();
if sci.is_none() {
let ctx = ScenarioContextItem(Mutex::new(C::default()));
self.inner.set(ctx);
self.hooks
.borrow_mut()
.push(Box::new(ScenarioContextHook::<C>::new()));
true
} else {
false
}
}
/// With the extracted immutable context, run the function f.
pub fn with<C, F, R>(&self, func: F, defuse_poison: bool) -> Result<R, StepError>
where
F: FnOnce(&C) -> Result<R, StepError>,
C: ContextElement,
{
self.with_mut(|c: &mut C| func(&*c), defuse_poison)
}
/// With the extracted mutable context, run the function f.
pub fn with_mut<C, F, R>(&self, func: F, defuse_poison: bool) -> Result<R, StepError>
where
F: FnOnce(&mut C) -> Result<R, StepError>,
C: ContextElement,
{
let sci: &ScenarioContextItem<C> = self
.inner
.try_get()
.ok_or("required context type not registered with scenario")?;
let mut lock = match sci.0.lock() {
Ok(lock) => lock,
Err(pe) => {
if defuse_poison {
pe.into_inner()
} else {
return Err("context poisoned by panic".into());
}
}
};
func(&mut lock)
}
}
/// The embodiment of a subplot scenario
///
/// Scenario objects are built up by the generated test functions and then run
/// to completion. In rare cases they may be built up and cached for reuse
/// for example if a scenario is a subroutine.
pub struct Scenario {
contexts: ScenarioContext,
steps: Vec<(ScenarioStep, Option<ScenarioStep>)>,
}
impl Scenario {
/// Create a new scenario with the given title
pub fn new(title: &str) -> Self {
Self {
contexts: ScenarioContext::new(title),
steps: Vec::new(),
}
}
/// Retrieve the scenario title
pub fn title(&self) -> &str {
self.contexts.title()
}
/// Add a scenario step, with optional cleanup step function.
pub fn add_step(&mut self, step: ScenarioStep, cleanup: Option<ScenarioStep>) {
step.register_contexts(self);
if let Some(s) = cleanup.as_ref() {
s.register_contexts(self)
}
self.steps.push((step, cleanup));
}
/// Register a type with the scenario contexts
pub fn register_context_type<C>(&self)
where
C: ContextElement,
{
if self.contexts.register_context_type::<C>() {
self.contexts
.with_mut(
|c: &mut C| {
c.created(self);
Ok(())
},
false,
)
.unwrap();
}
}
/// Run the scenario to completion.
///
/// Running the scenario to completion requires running each step in turn.
/// This will return the first encountered error, or unit if the scenario
/// runs cleanly.
///
/// # Panics
///
/// If any of the cleanup functions error, this will immediately panic.
///
pub fn run(self) -> Result<(), StepError> {
// Firstly, we start all the contexts
let mut ret = Ok(());
let mut highest_start = None;
for (i, hook) in self.contexts.hooks.borrow().iter().enumerate() {
let res = hook.scenario_starts(&self.contexts);
if res.is_err() {
ret = res;
break;
}
highest_start = Some(i);
}
if ret.is_ok() {
let mut highest = None;
for (i, step) in self.steps.iter().map(|(step, _)| step).enumerate() {
let mut highest_prep = None;
for (i, prep) in self.contexts.hooks.borrow().iter().enumerate() {
let res = prep.step_starts(&self.contexts, step.name());
if res.is_err() {
ret = res;
break;
}
highest_prep = Some(i);
}
if ret.is_ok() {
let res = step.call(&self.contexts, false);
if res.is_err() {
ret = res;
break;
}
highest = Some(i);
}
if let Some(n) = highest_prep {
for hookn in (0..=n).rev() {
let res = self.contexts.hooks.borrow()[hookn].step_stops(&self.contexts);
ret = ret.and(res)
}
}
}
if let Some(n) = highest {
for stepn in (0..=n).rev() {
if let (_, Some(cleanup)) = &self.steps[stepn] {
let res = cleanup.call(&self.contexts, true);
ret = ret.and(res);
}
}
}
}
if let Some(n) = highest_start {
for hookn in (0..=n).rev() {
let res = self.contexts.hooks.borrow()[hookn].scenario_stops(&self.contexts);
ret = ret.and(res);
}
}
ret
}
}