1 files changed, 86 insertions, 0 deletions
diff --git a/kotlinx-coroutines-core/common/test/flow/terminal/FirstTest.kt b/kotlinx-coroutines-core/common/test/flow/terminal/FirstTest.kt
new file mode 100644
index 00000000..e84d4c7b
--- /dev/null
+++ b/kotlinx-coroutines-core/common/test/flow/terminal/FirstTest.kt
@@ -0,0 +1,86 @@
+/*
+ * Copyright 2016-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
+ */
+
+package kotlinx.coroutines.flow
+
+import kotlinx.coroutines.*
+import kotlinx.coroutines.channels.*
+import kotlin.test.*
+
+class FirstTest : TestBase() {
+    @Test
+    fun testFirst() = runTest {
+        val flow = flowOf(1, 2, 3)
+        assertEquals(1, flow.first())
+    }
+
+    @Test
+    fun testNulls() = runTest {
+        val flow = flowOf(null, 1)
+        assertNull(flow.first())
+        assertNull(flow.first { it == null })
+        assertEquals(1, flow.first { it != null })
+    }
+
+    @Test
+    fun testFirstWithPredicate() = runTest {
+        val flow = flowOf(1, 2, 3)
+        assertEquals(1, flow.first { it > 0 })
+        assertEquals(2, flow.first { it > 1 })
+        assertFailsWith<NoSuchElementException> { flow.first { it > 3 } }
+    }
+
+    @Test
+    fun testFirstCancellation() = runTest {
+        val latch = Channel<Unit>()
+        val flow = flow {
+            coroutineScope {
+                launch {
+                    latch.send(Unit)
+                    hang { expect(1) }
+                }
+                emit(1)
+                emit(2)
+            }
+        }
+
+
+        val result = flow.first {
+            latch.receive()
+            true
+        }
+        assertEquals(1, result)
+        finish(2)
+    }
+
+    @Test
+    fun testEmptyFlow() = runTest {
+        assertFailsWith<NoSuchElementException> { emptyFlow<Int>().first() }
+        assertFailsWith<NoSuchElementException> { emptyFlow<Int>().first { true } }
+    }
+
+    @Test
+    fun testErrorCancelsUpstream() = runTest {
+        val latch = Channel<Unit>()
+        val flow = flow {
+            coroutineScope {
+                launch {
+                    latch.send(Unit)
+                    hang { expect(1) }
+                }
+                emit(1)
+            }
+        }
+
+        assertFailsWith<TestException> {
+            flow.first {
+                latch.receive()
+                throw TestException()
+            }
+        }
+
+        assertEquals(1, flow.first())
+        finish(2)
+    }
+}