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Add a test for discriminant_value #1021

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Apr 7, 2022
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62 changes: 62 additions & 0 deletions tests/kani/Intrinsics/discriminant_value.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,62 @@
// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0 OR MIT

// Check that `discriminant_value` returns the expected results
// for different cases
#![feature(core_intrinsics)]
use std::intrinsics::discriminant_value;

// A standard enum with variants containing fields
enum MyError {
Error1(i32),
Error2(&'static str),
Error3 { description: String, code: u32 },
}

#[kani::proof]
fn test_standard_enum() {
// Check that the values go from 0 to `num_variants - 1`
assert!(discriminant_value(&MyError::Error1) == 0);
assert!(discriminant_value(&MyError::Error2("bar")) == 1);
assert!(
discriminant_value(&MyError::Error3 { description: "some_error".to_string(), code: 3 })
== 2
);
}

// An enum that assigns constant values to some variants
enum Constants {
A = 2,
B = 5,
C,
}

#[kani::proof]
fn test_constants_enum() {
// Check that the values are equal to the constants assigned
assert!(discriminant_value(&Ordering::Less) == -1);
assert!(discriminant_value(&Ordering::Equal) == 0);
assert!(discriminant_value(&Ordering::Greater) == 1);
}

// An enum that assigns constant values (one of them negative) to all variants
enum Ordering {
Less = -1,
Equal = 0,
Greater = 1,
}

#[kani::proof]
fn test_ordering_enum() {
// Check that the values are equal to the constants assigned
// and the non-assigned value follows from the assigned ones
assert!(discriminant_value(&Constants::A) == 2);
assert!(discriminant_value(&Constants::B) == 5);
assert!(discriminant_value(&Constants::C) == 6);
}

#[kani::proof]
fn test_no_enum() {
// Check that the value is 0 if the type has no discriminant
assert!(discriminant_value(&2) == 0);
}