Refactors main function and enhances test suite

Refactors the main function for improved testability by extracting
the core logic into a new run function. Updates argument handling
and error reporting to use return codes instead of os.Exit.

Adds comprehensive test coverage for main functionality,
including integration tests and validation against edge cases.

Enhances README with updated code coverage and feature improvement lists.

Addresses improved maintainability and testability of the application.

Bumps version to 0.3.1

main.go

@@ -16,6 +16,12 @@ import (
 // It handles command-line arguments, sets up dependencies,
 // and coordinates the parsing and exporting of courses.
 func main() {
+	os.Exit(run(os.Args))
+}
+
+// run contains the main application logic and returns an exit code.
+// This function is testable as it doesn't call os.Exit directly.
+func run(args []string) int {
 	// Dependency injection setup
 	htmlCleaner := services.NewHTMLCleaner()
 	parser := services.NewArticulateParser()
@@ -23,20 +29,20 @@ func main() {
 	app := services.NewApp(parser, exporterFactory)
 
 	// Check for required command-line arguments
-	if len(os.Args) < 4 {
-		fmt.Printf("Usage: %s <source> <format> <output>\n", os.Args[0])
+	if len(args) < 4 {
+		fmt.Printf("Usage: %s <source> <format> <output>\n", args[0])
 		fmt.Printf("  source: URI or file path to the course\n")
 		fmt.Printf("  format: export format (%s)\n", joinStrings(app.GetSupportedFormats(), ", "))
 		fmt.Printf("  output: output file path\n")
 		fmt.Println("\nExample:")
-		fmt.Printf("  %s articulate-sample.json markdown output.md\n", os.Args[0])
-		fmt.Printf("  %s https://rise.articulate.com/share/xyz docx output.docx\n", os.Args[0])
-		os.Exit(1)
+		fmt.Printf("  %s articulate-sample.json markdown output.md\n", args[0])
+		fmt.Printf("  %s https://rise.articulate.com/share/xyz docx output.docx\n", args[0])
+		return 1
 	}
 
-	source := os.Args[1]
-	format := os.Args[2]
-	output := os.Args[3]
+	source := args[1]
+	format := args[2]
+	output := args[3]
 
 	var err error
 
@@ -48,10 +54,12 @@ func main() {
 	}
 
 	if err != nil {
-		log.Fatalf("Error processing course: %v", err)
+		log.Printf("Error processing course: %v", err)
+		return 1
 	}
 
 	fmt.Printf("Successfully exported course to %s\n", output)
+	return 0
 }
 
 // isURI checks if a string is a URI by looking for http:// or https:// prefixes.