mobile: Fix missing logging output in Swift integration tests (envoyproxy#36040)

In Swift, `print` goes to stdout buffering. The fix is to flush the
`stdout` and `stderr` before the end of the test.

See
swiftlang/swift-corelibs-xctest#422 (comment)

Risk Level: low (tests only)
Testing: CI
Docs Changes: n/a
Release Notes: n/a
Platform Specific Features: n/a

---------

Signed-off-by: Fredy Wijaya <fredyw@google.com>

Author: fredyw

mobile/test/swift/integration/CancelGRPCStreamTest.swift

@@ -11,6 +11,13 @@ final class CancelGRPCStreamTests: XCTestCase {
     register_test_extensions()
   }
 
+  override static func tearDown() {
+    super.tearDown()
+    // Flush the stdout and stderror to show the print output.
+    fflush(stdout)
+    fflush(stderr)
+  }
+
   func testCancelGRPCStream() {
     let filterName = "cancel_validation_filter"
 

mobile/test/swift/integration/CancelStreamTest.swift

@@ -11,6 +11,13 @@ final class CancelStreamTests: XCTestCase {
     register_test_extensions()
   }
 
+  override static func tearDown() {
+    super.tearDown()
+    // Flush the stdout and stderror to show the print output.
+    fflush(stdout)
+    fflush(stderr)
+  }
+
   func testCancelStream() {
     let filterName = "cancel_validation_filter"
 

mobile/test/swift/integration/EndToEndNetworkingTest.swift

@@ -10,6 +10,13 @@ final class EndToEndNetworkingTest: XCTestCase {
     register_test_extensions()
   }
 
+  override static func tearDown() {
+    super.tearDown()
+    // Flush the stdout and stderror to show the print output.
+    fflush(stdout)
+    fflush(stderr)
+  }
+
   func testNetworkRequestReturnsHeadersAndData() {
     EnvoyTestServer.startHttp1PlaintextServer()
     EnvoyTestServer.setHeadersAndData(

mobile/test/swift/integration/EngineApiTest.swift

@@ -9,6 +9,13 @@ final class EngineApiTest: XCTestCase {
     register_test_extensions()
   }
 
+  override static func tearDown() {
+    super.tearDown()
+    // Flush the stdout and stderror to show the print output.
+    fflush(stdout)
+    fflush(stderr)
+  }
+
   func testEngineApis() throws {
     let engineExpectation = self.expectation(description: "Engine Running")
 

mobile/test/swift/integration/FilterResetIdleTest.swift

@@ -11,6 +11,13 @@ final class FilterResetIdleTests: XCTestCase {
     register_test_extensions()
   }
 
+  override static func tearDown() {
+    super.tearDown()
+    // Flush the stdout and stderror to show the print output.
+    fflush(stdout)
+    fflush(stderr)
+  }
+
   func testFilterResetIdle() {
     let filterName = "reset_idle_test_filter"
 

mobile/test/swift/integration/GRPCReceiveErrorTest.swift

@@ -11,6 +11,13 @@ final class GRPCReceiveErrorTests: XCTestCase {
     register_test_extensions()
   }
 
+  override static func tearDown() {
+    super.tearDown()
+    // Flush the stdout and stderror to show the print output.
+    fflush(stdout)
+    fflush(stderr)
+  }
+
   func testReceiveError() {
     let filterName = "error_validation_filter"
 

mobile/test/swift/integration/IdleTimeoutTest.swift

@@ -11,6 +11,13 @@ final class IdleTimeoutTests: XCTestCase {
     register_test_extensions()
   }
 
+  override static func tearDown() {
+    super.tearDown()
+    // Flush the stdout and stderror to show the print output.
+    fflush(stdout)
+    fflush(stderr)
+  }
+
   func testIdleTimeout() {
     let filterName = "reset_idle_test_filter"
 

mobile/test/swift/integration/KeyValueStoreTest.swift

@@ -11,6 +11,13 @@ final class KeyValueStoreTests: XCTestCase {
     register_test_extensions()
   }
 
+  override static func tearDown() {
+    super.tearDown()
+    // Flush the stdout and stderror to show the print output.
+    fflush(stdout)
+    fflush(stderr)
+  }
+
   func testKeyValueStore() {
     // swiftlint:disable:next line_length
     let kvStoreType = "type.googleapis.com/envoymobile.extensions.filters.http.test_kv_store.TestKeyValueStore"

mobile/test/swift/integration/ReceiveDataTest.swift

@@ -11,6 +11,13 @@ final class ReceiveDataTests: XCTestCase {
     register_test_extensions()
   }
 
+  override static func tearDown() {
+    super.tearDown()
+    // Flush the stdout and stderror to show the print output.
+    fflush(stdout)
+    fflush(stderr)
+  }
+
   func testReceiveData() {
     let directResponseBody = "response_body"
     EnvoyTestServer.startHttp1PlaintextServer()

mobile/test/swift/integration/ReceiveErrorTest.swift

@@ -10,6 +10,13 @@ final class ReceiveErrorTests: XCTestCase {
     register_test_extensions()
   }
 
+  override static func tearDown() {
+    super.tearDown()
+    // Flush the stdout and stderror to show the print output.
+    fflush(stdout)
+    fflush(stderr)
+  }
+
   func testReceiveError() {
     let filterName = "error_validation_filter"
 
@@ -59,9 +66,6 @@ final class ReceiveErrorTests: XCTestCase {
       .setLogger { _, msg in
         print(msg, terminator: "")
       }
-      .setLogger { _, msg in
-          print(msg, terminator: "")
-      }
       .addPlatformFilter(
         name: filterName,
         factory: {