Explicit UTC settings and TZ tests

Sources/Confidence/ConfidenceValue.swift

@@ -21,10 +21,16 @@ public class ConfidenceValue: Equatable, Encodable {
         self.value = .double(double)
     }
 
+    /// `date` should have at least precision to the "day".
+    /// If a custom TimeZone is set for the input DateComponents, the internal
+    /// serializers will convert the input to the local TimeZone before extracting the date.
     public init(date: DateComponents) {
         self.value = .date(date)
     }
 
+    /// If a custom TimeZone is set for the input Date, the internal serializers will convert
+    /// the input to the local TimeZone before extracting the date (i.e. the local offset
+    /// information is maintained rather than the one customly set in Date).
     public init(timestamp: Date) {
         self.value = .timestamp(timestamp)
     }
@@ -211,17 +217,19 @@ extension ConfidenceValueInternal {
         case .boolean(let boolean):
             try container.encode(boolean)
         case .date(let dateComponents):
-            let dateFormatter = DateFormatter()
-            dateFormatter.dateFormat = "yyyy-MM-dd"
+            let dateFormatter = ISO8601DateFormatter()
+            dateFormatter.timeZone = TimeZone.current
+            dateFormatter.formatOptions = [.withFullDate]
             if let date = Calendar.current.date(from: dateComponents) {
                 try container.encode(dateFormatter.string(from: date))
             } else {
                 throw ConfidenceError.internalError(message: "Could not create date from components")
             }
         case .timestamp(let date):
-            let isoFormatter = ISO8601DateFormatter()
-            let formattedDate = isoFormatter.string(from: date)
-            try container.encode(formattedDate)
+            let timestampFormatter = ISO8601DateFormatter()
+            timestampFormatter.timeZone = TimeZone.current
+            let timestamp = timestampFormatter.string(from: date)
+            try container.encode(timestamp)
         case .structure(let structure):
             try container.encode(structure)
         case .list(let list):

Tests/ConfidenceTests/ConfidenceValueTests.swift

@@ -101,9 +101,9 @@ final class ConfidenceConfidenceValueTests: XCTestCase {
     func testEncodeDecode() throws {
         let formatter = DateFormatter()
         formatter.dateFormat = "yyyy-MM-dd HH:mm:ss"
-        formatter.timeZone = TimeZone(abbreviation: "UTC")
-        let date = try XCTUnwrap(formatter.date(from: "2022-01-01 12:00:00"))
-        let dateComponents = DateComponents(year: 2024, month: 4, day: 3)
+        formatter.timeZone = TimeZone(abbreviation: "EDT") // Verify TimeZone conversion
+        let date = try XCTUnwrap(formatter.date(from: "2024-04-05 16:00:00"))
+        var dateComponents = DateComponents(year: 2024, month: 4, day: 3)
 
         let value = ConfidenceValue(structure: ([
             "bool": ConfidenceValue(boolean: true),
@@ -119,6 +119,10 @@ final class ConfidenceConfidenceValueTests: XCTestCase {
         let encoder = JSONEncoder()
         encoder.outputFormatting = .sortedKeys
         let resultString = String(data: try encoder.encode(value), encoding: .utf8)
+
+        let isoFormatter = ISO8601DateFormatter()
+        isoFormatter.timeZone = TimeZone.current
+        let expectedSerializedTimestamp = isoFormatter.string(from: date)
         let expectedString = """
         {\"bool\":true,
         \"date\":\"2024-04-03\",
@@ -128,9 +132,11 @@ final class ConfidenceConfidenceValueTests: XCTestCase {
         \"null\":null,
         \"string\":\"value\",
         \"structure\":{\"int\":5},
-        \"timestamp\":\"2022-01-01T12:00:00Z\"}
+        \"timestamp\":\"\(expectedSerializedTimestamp)\"}
         """.replacingOccurrences(of: "\n", with: "") // Newlines were added for readability
 
+        // The "base" timestamp is in UTC, but the local offset is added (e.g. "+002").
+        XCTAssertTrue(expectedSerializedTimestamp.starts(with: "2024-04-05T22:00:00"))
         XCTAssertEqual(resultString, expectedString)
     }
 }