Introduce test for testing "raw" element creaation

web/core/src/jsTest/kotlin/elements/ElementsTests.kt

+/*
+ * Copyright 2020-2021 JetBrains s.r.o. and respective authors and developers.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE.txt file.
+ */
+
+package org.jetbrains.compose.web.core.tests.elements
+
+import androidx.compose.runtime.Composable
+import org.jetbrains.compose.web.attributes.AttrsBuilder
+import org.jetbrains.compose.web.attributes.Tag
+import org.jetbrains.compose.web.core.tests.runTest
+import org.jetbrains.compose.web.dom.ContentBuilder
+import org.jetbrains.compose.web.dom.TagElement
+import org.jetbrains.compose.web.dom.Text
+import org.w3c.dom.HTMLElement
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+
+class ElementsTests {
+    @Test
+    fun rawCreation() = runTest {
+        @Composable
+        fun CustomElement(
+                attrs: AttrsBuilder<Tag.Div>.() -> Unit,
+                content: ContentBuilder<HTMLElement>? = null
+        ) {
+            TagElement<Tag.Div, HTMLElement>(
+                tagName = "custom",
+                applyAttrs = attrs,
+                content
+            )
+        }
+
+        composition {
+            CustomElement({
+                id("container")
+            }) {
+                Text("CUSTOM")
+            }
+        }
+
+        assertEquals("<div><custom id=\"container\">CUSTOM</custom></div>", root.outerHTML)
+    }
+}
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