Fix how we check if a range expression covers one value. (#815)

My previous fix, #806, had the wrong logic to determine if a
confirmation's expected count as-a-`RangeExpression` had exactly one
value, so we were printing sub-optimal messages on test failures.
Specifically, this:

```swift
await confirmation(expectedCount: 1) { // transformed to 1...1
  // fail to confirm
}
```

Would report "1...1 time(s)" instead of "1 time".

### Checklist:

- [x] Code and documentation should follow the style of the [Style
Guide](https://github.com/apple/swift-testing/blob/main/Documentation/StyleGuide.md).
- [x] If public symbols are renamed or modified, DocC references should
be updated.

Author: grynspan

Sources/Testing/Issues/Issue.swift

@@ -204,7 +204,7 @@ extension Issue.Kind: CustomStringConvertible {
           // bound." That's sufficient for us to determine if the range contains
           // a single value.
           let upperBound = expected.first { $0 > lowerBound }
-          if let upperBound, upperBound > lowerBound && lowerBound == upperBound - 1 {
+          if upperBound == nil {
             return "Confirmation was confirmed \(actual.counting("time")), but expected to be confirmed \(lowerBound.counting("time"))"
           }
         }

Tests/TestingTests/ConfirmationTests.swift

@@ -51,12 +51,36 @@ struct ConfirmationTests {
     var configuration = Configuration()
     configuration.eventHandler = { event, _ in
       if case let .issueRecorded(issue) = event.kind {
-        #expect(String(describing: issue) != "")
+        #expect(String(describing: issue).contains("time(s)"))
       }
     }
 
     await Test {
       await confirmation(expectedCount: 1...) { _ in }
+      await confirmation(expectedCount: 1...2) { _ in }
+      await confirmation(expectedCount: 1..<3) { _ in }
+    }.run(configuration: configuration)
+  }
+
+  @Test func confirmationFailureCanBeDescribedAsSingleValue() async {
+    var configuration = Configuration()
+    configuration.eventHandler = { event, _ in
+      if case let .issueRecorded(issue) = event.kind {
+        #expect(!String(describing: issue).contains("time(s)"))
+      }
+    }
+
+    await Test {
+      await confirmation(expectedCount: 1...1) { _ in }
+      await confirmation(expectedCount: 1..<2) { _ in }
+      await confirmation(expectedCount: Int.max...Int.max) { _ in }
+#if !SWT_NO_EXIT_TESTS
+      await withKnownIssue("Crashes in Swift standard library (rdar://139568287)") {
+        await #expect(exitsWith: .success) {
+          await confirmation(expectedCount: Int.max...) { _ in }
+        }
+      }
+#endif
     }.run(configuration: configuration)
   }