Refactor StdioClientTransport tests

Author: kpavlov

kotlin-sdk-client/src/commonTest/kotlin/io/modelcontextprotocol/kotlin/sdk/client/stdio/StdioClientTransportErrorHandlingTest.kt

@@ -3,9 +3,12 @@ package io.modelcontextprotocol.kotlin.sdk.client.stdio
 import io.kotest.matchers.booleans.shouldBeFalse
 import io.kotest.matchers.shouldBe
 import io.modelcontextprotocol.kotlin.sdk.client.StdioClientTransport
+import kotlinx.atomicfu.atomic
+import kotlinx.atomicfu.update
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.test.runTest
 import kotlinx.io.Buffer
+import kotlinx.io.writeString
 import kotlin.test.Test
 import kotlin.time.Duration.Companion.milliseconds
 
@@ -20,6 +23,7 @@ class StdioClientTransportErrorHandlingTest {
         // Empty stderr = immediate EOF
 
         val inputBuffer = Buffer()
+        inputBuffer.writeString("""data: {"jsonrpc":"2.0","method":"ping","id":1}\n\n""")
         val outputBuffer = Buffer()
 
         val transport = StdioClientTransport(
@@ -28,16 +32,17 @@ class StdioClientTransportErrorHandlingTest {
             error = stderrBuffer,
         )
 
-        var closeCalled = false
-        transport.onClose { closeCalled = true }
+        val closeCalled = atomic(false)
+        transport.onClose { closeCalled.update { true } }
 
         transport.start()
-        delay(100.milliseconds)
+        delay(200.milliseconds)
 
         // Stderr EOF should not close transport
-        closeCalled.shouldBeFalse()
+        closeCalled.value shouldBe false
 
         transport.close()
+        closeCalled.value shouldBe true
     }
 
     @Test

kotlin-sdk-client/src/commonTest/kotlin/io/modelcontextprotocol/kotlin/sdk/client/stdio/StdioClientTransportLifecycleTest.kt

@@ -9,23 +9,27 @@ import io.modelcontextprotocol.kotlin.sdk.types.toJSON
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.test.runTest
 import kotlinx.io.Buffer
+import kotlin.test.BeforeTest
 import kotlin.test.Test
 import kotlin.time.Duration.Companion.milliseconds
 
 class StdioClientTransportLifecycleTest {
 
+    private lateinit var transport: StdioClientTransport
+
+    @BeforeTest
+    fun beforeEach() {
+        transport = createTransport()
+    }
+
     @Test
     fun `should throw when started twice`() = runTest {
-        val transport = createTransport()
-
         transport.start()
 
         val exception = shouldThrow<IllegalStateException> {
             transport.start()
         }
         exception.message shouldContain "already started"
-
-        transport.close()
     }
 
     @Test