Fix lint errors: add error checks for errcheck linter

- Add error check for JSON response in panic handler
- Remove duplicate defer CloseDB() call (handled in shutdown)
- Add error checks for all WriteField() calls in test files
- Add error checks for CreateFormFile() and Write() calls
- Fix golangci-lint Go 1.25 compatibility by installing from source

handlers/book_test.go

@@ -22,18 +22,37 @@ func TestUploadBook(t *testing.T) {
 	writer := multipart.NewWriter(body)
 
 	// Add form fields
-	writer.WriteField("book_name", "Test Book")
-	writer.WriteField("cost", "10.50")
-	writer.WriteField("price", "15.99")
-	writer.WriteField("quantity", "100")
-	writer.WriteField("publisher_author", "Test Publisher")
-	writer.WriteField("category", "Fiction")
+	if err := writer.WriteField("book_name", "Test Book"); err != nil {
+		t.Fatalf("Failed to write field: %v", err)
+	}
+	if err := writer.WriteField("cost", "10.50"); err != nil {
+		t.Fatalf("Failed to write field: %v", err)
+	}
+	if err := writer.WriteField("price", "15.99"); err != nil {
+		t.Fatalf("Failed to write field: %v", err)
+	}
+	if err := writer.WriteField("quantity", "100"); err != nil {
+		t.Fatalf("Failed to write field: %v", err)
+	}
+	if err := writer.WriteField("publisher_author", "Test Publisher"); err != nil {
+		t.Fatalf("Failed to write field: %v", err)
+	}
+	if err := writer.WriteField("category", "Fiction"); err != nil {
+		t.Fatalf("Failed to write field: %v", err)
+	}
 
 	// Add image file
-	part, _ := writer.CreateFormFile("image", "test.png")
-	part.Write([]byte("fake image data"))
+	part, err := writer.CreateFormFile("image", "test.png")
+	if err != nil {
+		t.Fatalf("Failed to create form file: %v", err)
+	}
+	if _, err := part.Write([]byte("fake image data")); err != nil {
+		t.Fatalf("Failed to write image data: %v", err)
+	}
 
-	writer.Close()
+	if err := writer.Close(); err != nil {
+		t.Fatalf("Failed to close writer: %v", err)
+	}
 
 	req := httptest.NewRequest("POST", "/api/books", body)
 	req.Header.Set("Content-Type", writer.FormDataContentType())
@@ -55,8 +74,12 @@ func TestUploadBook_ValidationErrors(t *testing.T) {
 	// Test missing required field
 	body := &bytes.Buffer{}
 	writer := multipart.NewWriter(body)
-	writer.WriteField("book_name", "") // Empty book name
-	writer.Close()
+	if err := writer.WriteField("book_name", ""); err != nil { // Empty book name
+		t.Fatalf("Failed to write field: %v", err)
+	}
+	if err := writer.Close(); err != nil {
+		t.Fatalf("Failed to close writer: %v", err)
+	}
 
 	req := httptest.NewRequest("POST", "/api/books", body)
 	req.Header.Set("Content-Type", writer.FormDataContentType())

handlers/stationery_test.go

@@ -22,18 +22,37 @@ func TestUploadStationery(t *testing.T) {
 	writer := multipart.NewWriter(body)
 
 	// Add form fields
-	writer.WriteField("stationery_name", "Test Pen")
-	writer.WriteField("cost", "2.50")
-	writer.WriteField("price", "5.99")
-	writer.WriteField("quantity", "200")
-	writer.WriteField("category", "Writing")
-	writer.WriteField("color", "Blue")
+	if err := writer.WriteField("stationery_name", "Test Pen"); err != nil {
+		t.Fatalf("Failed to write field: %v", err)
+	}
+	if err := writer.WriteField("cost", "2.50"); err != nil {
+		t.Fatalf("Failed to write field: %v", err)
+	}
+	if err := writer.WriteField("price", "5.99"); err != nil {
+		t.Fatalf("Failed to write field: %v", err)
+	}
+	if err := writer.WriteField("quantity", "200"); err != nil {
+		t.Fatalf("Failed to write field: %v", err)
+	}
+	if err := writer.WriteField("category", "Writing"); err != nil {
+		t.Fatalf("Failed to write field: %v", err)
+	}
+	if err := writer.WriteField("color", "Blue"); err != nil {
+		t.Fatalf("Failed to write field: %v", err)
+	}
 
 	// Add image file
-	part, _ := writer.CreateFormFile("image", "test.png")
-	part.Write([]byte("fake image data"))
+	part, err := writer.CreateFormFile("image", "test.png")
+	if err != nil {
+		t.Fatalf("Failed to create form file: %v", err)
+	}
+	if _, err := part.Write([]byte("fake image data")); err != nil {
+		t.Fatalf("Failed to write image data: %v", err)
+	}
 
-	writer.Close()
+	if err := writer.Close(); err != nil {
+		t.Fatalf("Failed to close writer: %v", err)
+	}
 
 	req := httptest.NewRequest("POST", "/api/stationery", body)
 	req.Header.Set("Content-Type", writer.FormDataContentType())
@@ -55,8 +74,12 @@ func TestUploadStationery_ValidationErrors(t *testing.T) {
 	// Test missing required field
 	body := &bytes.Buffer{}
 	writer := multipart.NewWriter(body)
-	writer.WriteField("stationery_name", "") // Empty stationery name
-	writer.Close()
+	if err := writer.WriteField("stationery_name", ""); err != nil { // Empty stationery name
+		t.Fatalf("Failed to write field: %v", err)
+	}
+	if err := writer.Close(); err != nil {
+		t.Fatalf("Failed to close writer: %v", err)
+	}
 
 	req := httptest.NewRequest("POST", "/api/stationery", body)
 	req.Header.Set("Content-Type", writer.FormDataContentType())