Make sure that on_before_session_ending is called (#3487)

* Make sure that `on_before_session_ending` is called

* Move the call above the validtor set being set

* Bump spec_version

substrate/srml/session/src/mock.rs

@@ -53,6 +53,8 @@ thread_local! {
 	pub static SESSION_CHANGED: RefCell<bool> = RefCell::new(false);
 	pub static TEST_SESSION_CHANGED: RefCell<bool> = RefCell::new(false);
 	pub static DISABLED: RefCell<bool> = RefCell::new(false);
+	// Stores if `on_before_session_end` was called
+	pub static BEFORE_SESSION_END_CALLED: RefCell<bool> = RefCell::new(false);
 }
 
 pub struct TestShouldEndSession;
@@ -81,6 +83,9 @@ impl SessionHandler<u64> for TestSessionHandler {
 	fn on_disabled(_validator_index: usize) {
 		DISABLED.with(|l| *l.borrow_mut() = true)
 	}
+	fn on_before_session_ending() {
+		BEFORE_SESSION_END_CALLED.with(|b| *b.borrow_mut() = true);
+	}
 }
 
 pub struct TestOnSessionEnding;
@@ -134,8 +139,17 @@ pub fn set_next_validators(next: Vec<u64>) {
 	NEXT_VALIDATORS.with(|v| *v.borrow_mut() = next);
 }
 
+pub fn before_session_end_called() -> bool {
+	BEFORE_SESSION_END_CALLED.with(|b| *b.borrow())
+}
+
+pub fn reset_before_session_end_called() {
+	BEFORE_SESSION_END_CALLED.with(|b| *b.borrow_mut() = false);
+}
+
 #[derive(Clone, Eq, PartialEq)]
 pub struct Test;
+
 parameter_types! {
 	pub const BlockHashCount: u64 = 250;
 	pub const MaximumBlockWeight: u32 = 1024;