Gradle, tests runner, output stream handler: don't treat flush as new line

#KT-31931 Fixed

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/internal/testing/TCServiceMessageOutputStreamHandler.kt

@@ -33,7 +33,7 @@ internal class TCServiceMessageOutputStreamHandler(
     @Throws(IOException::class)
     override fun close() {
         closed = true
-        flush()
+        flushLine()
     }
 
     override fun write(b: ByteArray, off: Int, len: Int) {
@@ -77,10 +77,6 @@ internal class TCServiceMessageOutputStreamHandler(
         }
     }
 
-    override fun flush() {
-        flushLine()
-    }
-
     private fun overflow() {
         val text = buffer.toString("utf-8")
 

libraries/tools/kotlin-gradle-plugin/src/test/kotlin/org/jetbrains/kotlin/gradle/internal/testing/TCServiceMessageOutputStreamHandlerTest.kt

@@ -64,6 +64,24 @@ class TCServiceMessageOutputStreamHandlerTest {
         assertEquals("[]", logString)
     }
 
+    @Test
+    fun testFlush() {
+        handler.write("xxx##teamc".toByteArray())
+        handler.flush()
+        handler.write("ity[testStarted]\n".toByteArray())
+        handler.write("yyy##teamcity[testStarted]".toByteArray())
+        handler.close()
+        assertEquals(
+            "TEXT: `xxx`\n" +
+                    "MESSAGE: `##teamcity[testStarted]`\n" +
+                    "TEXT: `\n`\n" + // this will be ignore in org.jetbrains.kotlin.gradle.internal.testing.TCServiceMessagesClient.regularText
+                    "TEXT: `yyy`\n" +
+                    "MESSAGE: `##teamcity[testStarted]`\n",
+            clientCalls
+        )
+        assertEquals("[]", logString)
+    }
+
     @Test
     fun testMessage() {
         handler.write("xxx##teamcity[testStarted]\n".toByteArray())