Implement Category API methods (GetAllCategories, GetCategory)

- GetAllCategories returns all categories for a project
- GetCategory returns a single category by ID
- Returns ErrCategoryNotFound for non-existent categories
- Added ErrCategoryNotFound to IsNotFound helper
- Comprehensive test coverage

categories_test.go

@@ -0,0 +1,166 @@
+package kanboard
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestClient_GetAllCategories(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		var req JSONRPCRequest
+		json.NewDecoder(r.Body).Decode(&req)
+
+		if req.Method != "getAllCategories" {
+			t.Errorf("expected method=getAllCategories, got %s", req.Method)
+		}
+
+		params := req.Params.(map[string]any)
+		if params["project_id"].(float64) != 1 {
+			t.Errorf("expected project_id=1, got %v", params["project_id"])
+		}
+
+		resp := JSONRPCResponse{
+			JSONRPC: "2.0",
+			ID:      req.ID,
+			Result: json.RawMessage(`[
+				{"id": "1", "name": "Bug", "project_id": "1", "color_id": "red"},
+				{"id": "2", "name": "Feature", "project_id": "1", "color_id": "blue"}
+			]`),
+		}
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer server.Close()
+
+	client := NewClient(server.URL).WithAPIToken("test-token")
+
+	categories, err := client.GetAllCategories(context.Background(), 1)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if len(categories) != 2 {
+		t.Errorf("expected 2 categories, got %d", len(categories))
+	}
+
+	if categories[0].Name != "Bug" {
+		t.Errorf("expected first category='Bug', got %s", categories[0].Name)
+	}
+	if categories[1].Name != "Feature" {
+		t.Errorf("expected second category='Feature', got %s", categories[1].Name)
+	}
+}
+
+func TestClient_GetAllCategories_Empty(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		var req JSONRPCRequest
+		json.NewDecoder(r.Body).Decode(&req)
+
+		resp := JSONRPCResponse{
+			JSONRPC: "2.0",
+			ID:      req.ID,
+			Result:  json.RawMessage(`[]`),
+		}
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer server.Close()
+
+	client := NewClient(server.URL).WithAPIToken("test-token")
+
+	categories, err := client.GetAllCategories(context.Background(), 1)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if len(categories) != 0 {
+		t.Errorf("expected 0 categories, got %d", len(categories))
+	}
+}
+
+func TestClient_GetCategory(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		var req JSONRPCRequest
+		json.NewDecoder(r.Body).Decode(&req)
+
+		if req.Method != "getCategory" {
+			t.Errorf("expected method=getCategory, got %s", req.Method)
+		}
+
+		params := req.Params.(map[string]any)
+		if params["category_id"].(float64) != 5 {
+			t.Errorf("expected category_id=5, got %v", params["category_id"])
+		}
+
+		resp := JSONRPCResponse{
+			JSONRPC: "2.0",
+			ID:      req.ID,
+			Result:  json.RawMessage(`{"id": "5", "name": "Bug", "project_id": "1", "color_id": "red"}`),
+		}
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer server.Close()
+
+	client := NewClient(server.URL).WithAPIToken("test-token")
+
+	category, err := client.GetCategory(context.Background(), 5)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if int(category.ID) != 5 {
+		t.Errorf("expected ID=5, got %d", category.ID)
+	}
+	if category.Name != "Bug" {
+		t.Errorf("expected name='Bug', got %s", category.Name)
+	}
+	if category.ColorID != "red" {
+		t.Errorf("expected color_id='red', got %s", category.ColorID)
+	}
+}
+
+func TestClient_GetCategory_NotFound(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		var req JSONRPCRequest
+		json.NewDecoder(r.Body).Decode(&req)
+
+		// Kanboard returns null for non-existent categories
+		resp := JSONRPCResponse{
+			JSONRPC: "2.0",
+			ID:      req.ID,
+			Result:  json.RawMessage(`null`),
+		}
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer server.Close()
+
+	client := NewClient(server.URL).WithAPIToken("test-token")
+
+	_, err := client.GetCategory(context.Background(), 999)
+	if err == nil {
+		t.Fatal("expected error for non-existent category")
+	}
+
+	if !errors.Is(err, ErrCategoryNotFound) {
+		t.Errorf("expected ErrCategoryNotFound, got %v", err)
+	}
+}
+
+func TestClient_GetAllCategories_ContextCanceled(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		select {}
+	}))
+	defer server.Close()
+
+	client := NewClient(server.URL).WithAPIToken("test-token")
+
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+
+	_, err := client.GetAllCategories(ctx, 1)
+	if err == nil {
+		t.Fatal("expected error due to canceled context")
+	}
+}