CORE Sensor Related Additional Unit Tests (#39)

# *Additional Tests on Bluetooth-related functionality*

## ♻️ Current situation & Problem
Our code coverage is lower than expected; there was no test on decoding
logic.


## ⚙️ Release Notes 

- Added tests on decoding logic.

## ✅ Testing
All tests pass.

## 📝 Code of Conduct & Contributing Guidelines 

By submitting creating this pull request, you agree to follow our [Code
of
Conduct](https://github.com/CS342/.github/blob/main/CODE_OF_CONDUCT.md)
and [Contributing
Guidelines](https://github.com/CS342/.github/blob/main/CONTRIBUTING.md):
- [X] I agree to follow the [Code of
Conduct](https://github.com/CS342/.github/blob/main/CODE_OF_CONDUCT.md)
and [Contributing
Guidelines](https://github.com/CS342/.github/blob/main/CONTRIBUTING.md).

Author: mmervecerit

NeutroFeverGuard.xcodeproj/project.pbxproj

@@ -77,6 +77,7 @@
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+		B0E1C5C32D80D3CB009CF90A /* SkinTemperatureDecodingTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = B0E1C5C22D80D3CB009CF90A /* SkinTemperatureDecodingTests.swift */; };
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@@ -160,6 +161,7 @@
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 		B0DF8DFB2D7C114900581A00 /* HealthDataFetchable.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = HealthDataFetchable.swift; sourceTree = "<group>"; };
+		B0E1C5C22D80D3CB009CF90A /* SkinTemperatureDecodingTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SkinTemperatureDecodingTests.swift; sourceTree = "<group>"; };
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 		C42C1C6A2D7A985B00EA417F /* MedicationManager.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = MedicationManager.swift; sourceTree = "<group>"; };
@@ -377,6 +379,7 @@
 			isa = PBXGroup;
 			children = (
 				B0DF8DF62D7BFEF600581A00 /* FeverMonitorTests.swift */,
+				B0E1C5C22D80D3CB009CF90A /* SkinTemperatureDecodingTests.swift */,
 				653A256128338800005D4D48 /* NeutroFeverGuardTests.swift */,
 				C4A367C72D73C1E1009923C9 /* DataErrorTests.swift */,
 				C4C8A3B22D71204200F313AE /* HelperFuncTests.swift */,
@@ -674,6 +677,7 @@
 			isa = PBXSourcesBuildPhase;
 			buildActionMask = 2147483647;
 			files = (
+				B0E1C5C32D80D3CB009CF90A /* SkinTemperatureDecodingTests.swift in Sources */,
 				C4A367C82D73C1EC009923C9 /* DataErrorTests.swift in Sources */,
 				B08E39F92D7C416000077929 /* FeverMonitoring.swift in Sources */,
 				EB02C6612D5D52E90035AA89 /* NeutroFeverGuardTests.swift in Sources */,

NeutroFeverGuardTests/SkinTemperatureDecodingTests.swift

@@ -0,0 +1,104 @@
+//
+// This source file is part of the NeutroFeverGuard based on the Stanford Spezi Template Application project
+//
+// SPDX-FileCopyrightText: 2025 Stanford University
+//
+// SPDX-License-Identifier: MIT
+//
+import Foundation
+@testable import NeutroFeverGuard
+import Testing
+
+@MainActor
+struct SkinTemperatureDecodingTests {
+    @Test("Decode valid Celsius temperature")
+    func testDecodeValidCelsiusTemperature() {
+        // Flags: 0x00 (Celsius, no timestamp)
+        let data: [UInt8] = [0x00, 0x42, 0x0E, 0x00, 0xFE]
+        let measurement = SkinTemperatureMeasurement(from: Data(data))
+
+        #expect(measurement != nil)
+        #expect(measurement?.temperature == 36.50)
+        #expect(measurement?.unit == .celsius)
+        #expect(measurement?.timestamp == nil)
+    }
+
+    @Test("Decode valid Fahrenheit temperature")
+    func testDecodeValidFahrenheitTemperature() {
+        // Flags: 0x01 (Fahrenheit, no timestamp)
+        let data: [UInt8] = [0x01, 0xDA, 0x03, 0x00, 0xFF]
+        let measurement = SkinTemperatureMeasurement(from: Data(data))
+
+        #expect(measurement != nil)
+        #expect(measurement?.temperature == 98.60)
+        #expect(measurement?.unit == .fahrenheit)
+        #expect(measurement?.timestamp == nil)
+    }
+
+    @Test("Handle sensor off-body NaN value")
+    func testDecodeSensorOffBody() {
+        // Flags: 0x00 (Celsius, no timestamp), Value: NaN (0x007FFFFF)
+        let data: [UInt8] = [0x00, 0xFF, 0xFF, 0x7F, 0x00]
+        let measurement = SkinTemperatureMeasurement(from: Data(data))
+
+        #expect(measurement == nil)
+    }
+
+    @Test("Decode temperature with timestamp")
+    func testDecodeTemperatureWithTimestamp() {
+        // Flags: 0x02 (Celsius + Timestamp)
+        // Temp: 37.20°C, Timestamp: 2025-03-10 14:30:45
+        let data: [UInt8] = [
+            0x02,       // Flags
+            0x88, 0x0E, 0x00, 0xFE, // Temperature: 37.20°C
+            0xE9, 0x07, // Year: 2025
+            0x03,       // Month: 3 (March)
+            0x0A,       // Day: 10
+            0x0E,       // Hour: 14
+            0x1E,       // Minute: 30
+            0x2D        // Second: 45
+        ]
+        let measurement = SkinTemperatureMeasurement(from: Data(data))
+
+        #expect(measurement != nil)
+        #expect(measurement?.temperature == 37.20)
+        #expect(measurement?.unit == .celsius)
+        #expect(measurement?.timestamp != nil)
+        
+        if let timestamp = measurement?.timestamp {
+            let calendar = Calendar.current
+            let components = calendar.dateComponents([.year, .month, .day, .hour, .minute, .second], from: timestamp)
+
+            #expect(components.year == 2025)
+            #expect(components.month == 3)
+            #expect(components.day == 10)
+            #expect(components.hour == 14)
+            #expect(components.minute == 30)
+            #expect(components.second == 45)
+        } else {
+            #expect(true, "Timestamp should not be nil")
+        }
+    }
+
+    @Test("Handle incomplete data")
+    func testDecodeIncompleteData() {
+        let incompleteData: [UInt8] = [0x00, 0x42] // Too short
+        let measurement = SkinTemperatureMeasurement(from: Data(incompleteData))
+
+        #expect(measurement == nil)
+    }
+
+    @Test("Handle corrupted timestamp data")
+    func testDecodeInvalidTimestamp() {
+        let data: [UInt8] = [
+            0x02,       // Flags (Celsius + Timestamp present)
+            0x88, 0x2E, 0x00, 0x00, // Temperature: 37.20°C
+            0xE9, 0x07, // Year: 2025
+            0x03        // Month: 3 (missing Day, Hour, Min, Sec)
+        ]
+        let measurement = SkinTemperatureMeasurement(from: Data(data))
+
+        #expect(measurement != nil)
+        #expect(measurement?.timestamp == nil)
+    }
+}