Fix compatiblity with older compilers.

Tests/CacheTests.swift

@@ -83,11 +83,15 @@ class CacheTestCase: BaseTestCase {
 
         urlCache = {
             let capacity = 50 * 1024 * 1024 // MBs
+            #if swift(>=5.1)
             if #available(OSX 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, *) {
                 return URLCache(memoryCapacity: capacity, diskCapacity: capacity)
             } else {
                 return URLCache(memoryCapacity: capacity, diskCapacity: capacity, diskPath: nil)
             }
+            #else
+            return URLCache(memoryCapacity: capacity, diskCapacity: capacity, diskPath: nil)
+            #endif
         }()
 
         manager = {

Tests/CachedResponseHandlerTests.swift

@@ -199,12 +199,16 @@ final class CachedResponseHandlerTestCase: BaseTestCase {
         let configuration = URLSessionConfiguration.af.default
         let capacity = 100_000_000
         let cache: URLCache
+        #if swift(>=5.1)
         if #available(OSX 10.15, iOS 13.0, watchOS 6.0, tvOS 13.0, *) {
             let directory = FileManager.default.temporaryDirectory.appendingPathComponent(UUID().uuidString)
             cache = URLCache(memoryCapacity: capacity, diskCapacity: capacity, directory: directory)
         } else {
             cache = URLCache(memoryCapacity: capacity, diskCapacity: capacity, diskPath: UUID().uuidString)
         }
+        #else
+        cache = URLCache(memoryCapacity: capacity, diskCapacity: capacity, diskPath: UUID().uuidString)
+        #endif
         configuration.urlCache = cache
 
         return Session(configuration: configuration, cachedResponseHandler: handler)

Tests/TLSEvaluationTests.swift

@@ -145,7 +145,7 @@ final class TLSEvaluationExpiredLeafCertificateTestCase: BaseTestCase {
         XCTAssertNotNil(error, "error should not be nil")
 
         XCTAssertEqual(error?.isServerTrustEvaluationError, true)
-        if case let .serverTrustEvaluationFailed(reason) = error {
+        if case let .serverTrustEvaluationFailed(reason)? = error {
             XCTAssertTrue(reason.isHostValidationFailed, "should be .hostValidationFailed")
         } else {
             XCTFail("error should be .serverTrustEvaluationFailed")
@@ -211,7 +211,7 @@ final class TLSEvaluationExpiredLeafCertificateTestCase: BaseTestCase {
         XCTAssertNotNil(error, "error should not be nil")
         XCTAssertEqual(error?.isServerTrustEvaluationError, true)
 
-        if case let .serverTrustEvaluationFailed(reason) = error {
+        if case let .serverTrustEvaluationFailed(reason)? = error {
             XCTAssertTrue(reason.isDefaultEvaluationFailed, "should be .defaultEvaluationFailed")
         } else {
             XCTFail("error should be .serverTrustEvaluationFailed")
@@ -243,7 +243,7 @@ final class TLSEvaluationExpiredLeafCertificateTestCase: BaseTestCase {
         XCTAssertNotNil(error, "error should not be nil")
         XCTAssertEqual(error?.isServerTrustEvaluationError, true)
 
-        if case let .serverTrustEvaluationFailed(reason) = error {
+        if case let .serverTrustEvaluationFailed(reason)? = error {
             XCTAssertTrue(reason.isDefaultEvaluationFailed, "should be .defaultEvaluationFailed")
         } else {
             XCTFail("error should be .serverTrustEvaluationFailed")
@@ -276,7 +276,7 @@ final class TLSEvaluationExpiredLeafCertificateTestCase: BaseTestCase {
         XCTAssertNotNil(error, "error should not be nil")
         XCTAssertEqual(error?.isServerTrustEvaluationError, true)
 
-        if case let .serverTrustEvaluationFailed(reason) = error {
+        if case let .serverTrustEvaluationFailed(reason)? = error {
             XCTAssertTrue(reason.isDefaultEvaluationFailed, "should be .defaultEvaluationFailed")
         } else {
             XCTFail("error should be .serverTrustEvaluationFailed")
@@ -311,7 +311,7 @@ final class TLSEvaluationExpiredLeafCertificateTestCase: BaseTestCase {
         XCTAssertNotNil(error, "error should not be nil")
         XCTAssertEqual(error?.isServerTrustEvaluationError, true)
 
-        if case let .serverTrustEvaluationFailed(reason) = error {
+        if case let .serverTrustEvaluationFailed(reason)? = error {
             XCTAssertTrue(reason.isDefaultEvaluationFailed, "should be .defaultEvaluationFailed")
         } else {
             XCTFail("error should be .serverTrustEvaluationFailed")
@@ -420,7 +420,7 @@ final class TLSEvaluationExpiredLeafCertificateTestCase: BaseTestCase {
         XCTAssertNotNil(error, "error should not be nil")
         XCTAssertEqual(error?.isServerTrustEvaluationError, true)
 
-        if case let .serverTrustEvaluationFailed(reason) = error {
+        if case let .serverTrustEvaluationFailed(reason)? = error {
             XCTAssertTrue(reason.isDefaultEvaluationFailed, "should be .defaultEvaluationFailed")
         } else {
             XCTFail("error should be .serverTrustEvaluationFailed")