Support operator overloads for beNil matcher

Author: ikesyo

Sources/Nimble/Matchers/BeNil.swift

@@ -6,6 +6,21 @@ public func beNil<T>() -> Predicate<T> {
     }
 }
 
+extension Expectation {
+    /// Represents `nil` value to be used with the operator overloads for `beNil`.
+    public struct Nil: ExpressibleByNilLiteral {
+        public init(nilLiteral: ()) {}
+    }
+
+    public static func == (lhs: Expectation, rhs: Expectation.Nil) {
+        lhs.to(beNil())
+    }
+
+    public static func != (lhs: Expectation, rhs: Expectation.Nil) {
+        lhs.toNot(beNil())
+    }
+}
+
 #if canImport(Darwin)
 import Foundation
 

Tests/NimbleTests/Matchers/BeNilTest.swift

@@ -8,15 +8,32 @@ final class BeNilTest: XCTestCase {
 
     func testBeNil() {
         expect(nil as Int?).to(beNil())
+        expect(nil as Int?) == nil
+
         expect(1 as Int?).toNot(beNil())
+        expect(1 as Int?) != nil
+
         expect(self.producesNil()).to(beNil())
+        expect(self.producesNil()) == nil
 
-        failsWithErrorMessage("expected to not be nil, got <nil>") {
-            expect(nil as Int?).toNot(beNil())
+        do {
+            let message = "expected to not be nil, got <nil>"
+            failsWithErrorMessage(message) {
+                expect(nil as Int?).toNot(beNil())
+            }
+            failsWithErrorMessage(message) {
+                expect(nil as Int?) != nil
+            }
         }
 
-        failsWithErrorMessage("expected to be nil, got <1>") {
-            expect(1 as Int?).to(beNil())
+        do {
+            let message = "expected to be nil, got <1>"
+            failsWithErrorMessage(message) {
+                expect(1 as Int?).to(beNil())
+            }
+            failsWithErrorMessage(message) {
+                expect(1 as Int?) == nil
+            }
         }
     }
 }