Add execute_with to TestExternalities (#3793)

This function executes the given closure in a context where the test
externalities are set. This makes the srml tests easier to write, as the
test externalities need to be created anyway.

substrate/core/sr-primitives/src/lib.rs

@@ -73,9 +73,6 @@ pub use sr_arithmetic::helpers_128bit;
 /// Re-export big_uint stiff.
 pub use sr_arithmetic::biguint;
 
-#[cfg(feature = "std")]
-pub use externalities::set_and_run_with_externalities;
-
 /// An abstraction over justification for a block's validity under a consensus algorithm.
 ///
 /// Essentially a finality proof. The exact formulation will vary between consensus

substrate/core/sr-primitives/src/offchain/http.rs

@@ -512,7 +512,6 @@ impl<'a> HeadersIterator<'a> {
 #[cfg(test)]
 mod tests {
 	use super::*;
-	use crate::set_and_run_with_externalities;
 	use runtime_io::TestExternalities;
 	use substrate_offchain::testing;
 	use primitives::offchain::OffchainExt;
@@ -523,7 +522,7 @@ mod tests {
 		let mut t = TestExternalities::default();
 		t.register_extension(OffchainExt::new(offchain));
 
-		set_and_run_with_externalities(&mut t, || {
+		t.execute_with(|| {
 			let request: Request = Request::get("http://localhost:1234");
 			let pending = request
 				.add_header("X-Auth", "hunter2")
@@ -564,7 +563,7 @@ mod tests {
 		let mut t = TestExternalities::default();
 		t.register_extension(OffchainExt::new(offchain));
 
-		set_and_run_with_externalities(&mut t, || {
+		t.execute_with(|| {
 			let pending = Request::default()
 				.method(Method::Post)
 				.url("http://localhost:1234")