first (#831)

* single vs first

* commit

* commit

* commit

Author: kanake10

core-kotlin-modules/core-kotlin-concurrency-3/src/test/java/com/baeldung/comparefirstandsingleUnitTests/FirstUnitTest.kt

@@ -0,0 +1,33 @@
+package com.baeldung.comparefirstandsingleUnitTests
+
+import junit.framework.Assert.assertEquals
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.emptyFlow
+import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.flow.flowOf
+import kotlinx.coroutines.runBlocking
+import org.junit.jupiter.api.Test
+import kotlin.test.assertFailsWith
+
+
+class FirstUnitTest {
+
+    @Test
+    fun testFirstValue() = runBlocking {
+        val multipleValuesFlow = flowOf(1, 2, 3)
+        val firstValue = multipleValuesFlow.first()
+        assertEquals(1, firstValue)
+    }
+
+    @Test
+    fun testFirstValueFromEmptyFlow() = runBlocking {
+        val emptyFlow = emptyFlow<Int>()
+        val exception = assertFailsWith<NoSuchElementException> {
+            runBlocking {
+                emptyFlow.first()
+            }
+        }
+        assertEquals("Expected at least one element", exception.message)
+    }
+
+}

core-kotlin-modules/core-kotlin-concurrency-3/src/test/java/com/baeldung/comparefirstandsingleUnitTests/SingleFunctionUnitTest.kt

@@ -0,0 +1,39 @@
+package com.baeldung.comparefirstandsingleUnitTests
+
+import junit.framework.Assert.assertEquals
+import kotlinx.coroutines.flow.flowOf
+import kotlinx.coroutines.flow.single
+import kotlinx.coroutines.runBlocking
+import org.junit.jupiter.api.Test
+import kotlin.test.assertFailsWith
+class SingleFunctionUnitTest {
+
+    @Test
+    fun testSingleValue() = runBlocking {
+        val multipleValuesFlow = flowOf(42)
+        val singleValue = multipleValuesFlow.single()
+        assertEquals(42, singleValue)
+    }
+
+    @Test
+    fun testExceptionForMultipleValues() = runBlocking {
+        val multipleValues = flowOf(42, 43, 44)
+        val exception = assertFailsWith<IllegalArgumentException> {
+            runBlocking {
+                multipleValues.single()
+            }
+        }
+        assertEquals("Flow has more than one element", exception.message)
+    }
+
+    @Test
+    fun testIllegalArgumentException() = runBlocking {
+        val emptyFlow = flowOf<Int>()
+        val exception = assertFailsWith<NoSuchElementException> {
+            runBlocking {
+                emptyFlow.single()
+            }
+        }
+        assertEquals("Flow is empty", exception.message)
+    }
+}