Add tests for if-else statement

Author: fwcd

Tests/SwiftSyntaxBuilderTest/IfStmtTests.swift

@@ -0,0 +1,39 @@
+import XCTest
+import SwiftSyntax
+import SwiftSyntaxBuilder
+
+final class IfStmtTests: XCTestCase {
+  func testEmptyIfStmt() {
+    // Use the convenience initializer from IfStmtConvenienceInitializers. This is
+    // disambiguated by the absence of a labelName parameter and the use of a
+    // trailing closure.
+    let buildable = IfStmt(conditions: ExprList([BooleanLiteralExpr(false)])) {}
+    let syntax = buildable.buildSyntax(format: Format())
+    XCTAssertEqual(syntax.description, """
+      if false  {
+      }
+      """)
+  }
+
+  func testIfElseStmt() {
+    // Use the convenience initializer from IfStmtConvenienceInitializers
+    // with an else branch expressed by a second trailing closure.
+    let buildable = IfStmt(conditions: ExprList([BooleanLiteralExpr(true)])) {
+      FunctionCallExpr("print") {
+        TupleExprElement(expression: StringLiteralExpr("Hello from the if-branch!"))
+      }
+    } elseBody: {
+      FunctionCallExpr("print") {
+        TupleExprElement(expression: StringLiteralExpr("Hello from the else-branch!"))
+      }
+    }
+    let syntax = buildable.buildSyntax(format: Format())
+    XCTAssertEqual(syntax.description, """
+      if true  {
+          print("Hello from the if-branch!")
+      } else {
+          print("Hello from the else-branch!")
+      }
+      """)
+  }
+}