Add printFlow method

dachlatten-flow/src/main/java/de/sipgate/waffeleisen/flow/PrintFlow.kt

@@ -0,0 +1,14 @@
+package de.sipgate.waffeleisen.flow
+
+import android.util.Log
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.map
+
+inline fun <T> Flow<T?>.printFlow(
+    tag: String = "from flow",
+    crossinline printFunc: (String) -> Unit = { content -> Log.d(tag, content) },
+    crossinline stringFunc: (T?) -> String? = { it.toString() }
+) = map {
+    printFunc(stringFunc(it) ?: "null")
+    it
+}

dachlatten-flow/src/test/java/de/sipgate/waffeleisen/flow/PrintFlowKtTest.kt

@@ -0,0 +1,76 @@
+package de.sipgate.waffeleisen.flow
+
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.collect
+import kotlinx.coroutines.flow.flowOf
+import kotlinx.coroutines.flow.map
+import kotlinx.coroutines.test.runTest
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Test
+
+class PrintFlowKtTest {
+
+    @Test
+    fun printFlowPassesThroughValuesTransparently() = runTest {
+        val flow = flowOf("first", "second", "third")
+
+        val result = flow
+            .printFlow(printFunc = { println(it) })
+            .collectAsList()
+
+        assertEquals(listOf("first", "second", "third"), result)
+    }
+
+    @Test
+    fun printFlowExecutesPrintFuncOnceForEachEmittedValue() = runTest {
+        val flow = flowOf("first", "second", "third")
+
+        val result = mutableListOf<String>()
+        flow.printFlow(printFunc = { result.add(it) }).collect()
+
+        assertEquals(listOf("first", "second", "third"), result.toList())
+    }
+
+    @Test
+    fun printFlowExecutesStringFuncForEachEmittedValue() = runTest {
+        val flow = flowOf("first", "second", "third")
+
+        val result = mutableListOf<String>()
+        flow.printFlow(
+            printFunc = { /* dummy */ },
+            stringFunc = { result.add(it!!); it }
+        ).collect()
+
+        assertEquals(listOf("first", "second", "third"), result.toList())
+    }
+
+    @Test
+    fun printFlowCallsToStringByDefault() = runTest {
+        data class SomeData(
+            val aProperty: String,
+            val bProperty: Boolean
+        )
+
+        val flow = flowOf(
+            SomeData("asdf", true),
+            SomeData("wah", false)
+        )
+
+        val stringBuffer = StringBuffer()
+        flow.printFlow(printFunc = { stringBuffer.append(it).append("\n") })
+            .collect()
+
+        val expected = """
+            SomeData(aProperty=asdf, bProperty=true)
+            SomeData(aProperty=wah, bProperty=false)
+
+        """.trimIndent()
+
+        assertEquals(expected, stringBuffer.toString())
+    }
+
+    private suspend fun <T> Flow<T>.collectAsList() =
+        mutableListOf<T>().apply {
+            this@collectAsList.map(this::add).collect()
+        }
+}