XCTAssertEqualWithAccuracy behavor does not match true XCTest.framework

The accuracy threshold check only works with unsigned numbers, however the distanceTo method we get from Strideable works in terms of offsets which can be negative. We need to take the absolute value of the distance.

This issue was causing tests for swiftlang/swift-corelibs-foundation#37 to fail.

Author: mattrajca

XCTest/XCTest.swift

@@ -177,7 +177,7 @@ public func XCTAssertEqual<T, U : Equatable>(@autoclosure expression1: () -> [T
 }
 
 public func XCTAssertEqualWithAccuracy<T : FloatingPointType>(@autoclosure expression1: () -> T, @autoclosure _ expression2: () -> T, accuracy: T, _ message: String = "", file: StaticString = __FILE__, line: UInt = __LINE__) {
-    XCTAssert(expression1().distanceTo(expression2()) <= accuracy.distanceTo(T(0)), message, file: file, line: line)
+    XCTAssert(abs(expression1().distanceTo(expression2())) <= abs(accuracy.distanceTo(T(0))), message, file: file, line: line)
 }
 
 public func XCTAssertFalse(@autoclosure expression: () -> BooleanType, _ message: String = "", file: StaticString = __FILE__, line: UInt = __LINE__) {
@@ -225,7 +225,7 @@ public func XCTAssertNotEqual<T, U : Equatable>(@autoclosure expression1: () ->
 }
 
 public func XCTAssertNotEqualWithAccuracy<T : FloatingPointType>(@autoclosure expression1: () -> T, @autoclosure _ expression2: () -> T, _ accuracy: T, _ message: String = "", file: StaticString = __FILE__, line: UInt = __LINE__) {
-    XCTAssert(expression1().distanceTo(expression2()) > accuracy.distanceTo(T(0)), message, file: file, line: line)
+    XCTAssert(abs(expression1().distanceTo(expression2())) > abs(accuracy.distanceTo(T(0))), message, file: file, line: line)
 }
 
 public func XCTAssertNotNil(@autoclosure expression: () -> Any?, _ message: String = "", file: StaticString = __FILE__, line: UInt = __LINE__) {