Use "helm" filtype first for vim modeline + tests

"helm" can be managed by vim/neovim plugins, so it's a good idea to add
it as default, then use "gotmpl.yaml".

Add basic tests...

generator/basic_test.go

@@ -0,0 +1,57 @@
+package generator
+
+import (
+	"log"
+	"os"
+	"testing"
+
+	"sigs.k8s.io/yaml"
+)
+
+func setup(content string) string {
+	// write the _compose_file in temporary directory
+	tmpDir, err := os.MkdirTemp("", "katenary")
+	if err != nil {
+		panic(err)
+	}
+	os.WriteFile(tmpDir+"/compose.yml", []byte(content), 0o644)
+	return tmpDir
+}
+
+func teardown(tmpDir string) {
+	// remove the temporary directory
+	log.Println("Removing temporary directory: ", tmpDir)
+	if err := os.RemoveAll(tmpDir); err != nil {
+		panic(err)
+	}
+}
+
+func TestGenerate(t *testing.T) {
+	_compose_file := `
+services:
+    web:
+        image: nginx:1.29
+`
+	tmpDir := setup(_compose_file)
+	defer teardown(tmpDir)
+
+	currentDir, _ := os.Getwd()
+	os.Chdir(tmpDir)
+	defer os.Chdir(currentDir)
+
+	output := _compile_test(t)
+
+	dt := DeploymentTest{}
+	if err := yaml.Unmarshal([]byte(output), &dt); err != nil {
+		t.Errorf("Failed to unmarshal the output: %s", err)
+	}
+
+	if dt.Spec.Replicas != 1 {
+		t.Errorf("Expected replicas to be 1, got %d", dt.Spec.Replicas)
+		t.Errorf("Output: %s", output)
+	}
+
+	if dt.Spec.Template.Spec.Containers[0].Image != "nginx:1.29" {
+		t.Errorf("Expected image to be nginx:1.29, got %s", dt.Spec.Template.Spec.Containers[0].Image)
+	}
+}