Added some tests

Tests/UnitsTests/UnitsTests.swift

@@ -1,10 +1,123 @@
 import Testing
 
-@testable import Units
+@testable import Units  // Assuming your library is in a module named 'Units'
 
-@Test func example() async throws {
-	// Write your test here and use APIs like `#expect(...)` to check expected conditions.
-	if let tenKilos = 10["kg"] {
-		print(tenKilos[tenKilos.unit]!)
-	}
+@Test func unitCreationSubscriptTests() async throws {
+	// Test creating UnitValue using string subscript on numeric literals
+	let tenKilosByString = 10.0["kg"]
+	#expect(tenKilosByString != nil)
+	#expect(tenKilosByString?.value == 10.0)
+	#expect(tenKilosByString?.unit == .kilogram)
+	print("Created 10 kg by string subscript: \(String(describing: tenKilosByString))")
+
+	let fiveMetersByString = 5.0["m"]
+	#expect(fiveMetersByString != nil)
+	#expect(fiveMetersByString?.value == 5.0)
+	#expect(fiveMetersByString?.unit == .meter)
+	print("Created 5 m by string subscript: \(String(describing: fiveMetersByString))")
+
+	// Test creating UnitValue using enum subscript on numeric literals
+	let twentyLitersByEnum = 20.0[.liter]
+	#expect(twentyLitersByEnum.value == 20.0)
+	#expect(twentyLitersByEnum.unit == .liter)
+	print("Created 20 L by enum subscript: \(twentyLitersByEnum)")
+
+	let thirtySecondsByEnum = 30.0[.second]
+	#expect(thirtySecondsByEnum.value == 30.0)
+	#expect(thirtySecondsByEnum.unit == .second)
+	print("Created 30 s by enum subscript: \(thirtySecondsByEnum)")
+
+	// Test invalid unit string for creation
+	let invalidUnitCreation = 100.0["xyz"]
+	#expect(invalidUnitCreation == nil)
+	print(
+		"Attempted invalid unit creation (should be nil): \(String(describing: invalidUnitCreation))"
+	)
+}
+
+@Test func unitConversionSubscriptTests() async throws {
+	// Test conversion using string subscript on UnitValue
+	if let tenKilos = 10.0["kg"] {
+		let pounds = tenKilos["lbs"]
+		#expect(pounds != nil)
+		#expect(pounds?.value == 22.046226218487757)  // Exact conversion value
+		#expect(pounds?.unit == .pound)
+		print("10 kg to lbs by string subscript: \(String(describing: pounds))")
+	} else {
+		#expect(false, "Failed to create initial 10 kg unit.")
+	}
+
+	// Test conversion using enum subscript on UnitValue
+	let fiveMeters = 5.0.m
+	let feet = fiveMeters[.foot]
+	#expect(feet != nil)
+	#expect(feet?.value == 16.404199475065617)  // Exact conversion value
+	#expect(feet?.unit == .foot)
+	print("5 m to ft by enum subscript: \(String(describing: feet))")
+
+	// Test chained conversions
+	if let initialValue = 100.0["km"] {
+		let miles = initialValue["mi"]
+		#expect(miles != nil)
+		#expect(miles?.value == 62.13711922373339)  // Exact conversion value
+		#expect(miles?.unit == .mile)
+		print("100 km to mi (chained string subscript): \(String(describing: miles))")
+
+		let feetFromMiles = miles?["ft"]
+		#expect(feetFromMiles != nil)
+		#expect(feetFromMiles?.value == 328083.9895013123)  // Exact conversion value (100km -> mi -> ft)
+		#expect(feetFromMiles?.unit == .foot)
+		print("100 km to mi to ft (chained string subscript): \(String(describing: feetFromMiles))")
+	} else {
+		#expect(false, "Failed to create initial 100 km unit.")
+	}
+
+	// Test invalid conversion (different categories)
+	let tenKilos = 10.0.kg
+	let metersFromKilos = tenKilos["m"]
+	#expect(metersFromKilos == nil)
+	print(
+		"Attempted invalid conversion (mass to length, should be nil): \(String(describing: metersFromKilos))"
+	)
+
+	// Test invalid target unit string for conversion
+	let invalidTargetConversion = tenKilos["xyz"]
+	#expect(invalidTargetConversion == nil)
+	print(
+		"Attempted conversion to invalid unit string (should be nil): \(String(describing: invalidTargetConversion))"
+	)
+}
+
+@Test func temperatureConversionSubscriptTests() async throws {
+	// Test Celsius to Fahrenheit
+	let twentyFiveC = 25.0[.celsius]
+	let fahrenheitFromC = twentyFiveC[.fahrenheit]
+	#expect(fahrenheitFromC != nil)
+	#expect(fahrenheitFromC?.value == 77.0)
+	#expect(fahrenheitFromC?.unit == .fahrenheit)
+	print("25°C to °F: \(String(describing: fahrenheitFromC))")
+
+	// Test Fahrenheit to Celsius
+	let ninetyEightF = 98.6[.fahrenheit]
+	let celsiusFromF = ninetyEightF[.celsius]
+	#expect(celsiusFromF != nil)
+	#expect(celsiusFromF?.value == 37.0)
+	#expect(celsiusFromF?.unit == .celsius)
+	print("98.6°F to °C: \(String(describing: celsiusFromF))")
+
+	// Test Celsius to Kelvin
+	let zeroC = 0.0[.celsius]
+	let kelvinFromC = zeroC[.kelvin]
+	#expect(kelvinFromC != nil)
+	#expect(kelvinFromC?.value == 273.15)
+	#expect(kelvinFromC?.unit == .kelvin)
+	print("0°C to K: \(String(describing: kelvinFromC))")
+
+	// Test Kelvin to Celsius
+	let twoSeventyThreeK = 273.15[.kelvin]
+	let celsiusFromK = twoSeventyThreeK[.celsius]
+	#expect(celsiusFromK != nil)
+	#expect(celsiusFromK?.value == 0.0)
+	#expect(celsiusFromK?.unit == .celsius)
+	print("273.15 K to °C: \(String(describing: celsiusFromK))")
 }