Implement Column API methods (GetColumns, GetColumn)

- GetColumns returns all columns for a project, sorted by position
- GetColumn returns a single column by ID
- Returns ErrColumnNotFound for non-existent columns
- Comprehensive test coverage including edge cases

columns_test.go

@@ -0,0 +1,172 @@
+package kanboard
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestClient_GetColumns(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 != "getColumns" {
+			t.Errorf("expected method=getColumns, 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"])
+		}
+
+		// Return columns in wrong order to test sorting
+		resp := JSONRPCResponse{
+			JSONRPC: "2.0",
+			ID:      req.ID,
+			Result: json.RawMessage(`[
+				{"id": "3", "title": "Done", "position": "3", "project_id": "1", "task_limit": "0"},
+				{"id": "1", "title": "Backlog", "position": "1", "project_id": "1", "task_limit": "10"},
+				{"id": "2", "title": "In Progress", "position": "2", "project_id": "1", "task_limit": "5"}
+			]`),
+		}
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer server.Close()
+
+	client := NewClient(server.URL).WithAPIToken("test-token")
+
+	columns, err := client.GetColumns(context.Background(), 1)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if len(columns) != 3 {
+		t.Errorf("expected 3 columns, got %d", len(columns))
+	}
+
+	// Verify sorted by position
+	if columns[0].Title != "Backlog" {
+		t.Errorf("expected first column='Backlog', got %s", columns[0].Title)
+	}
+	if columns[1].Title != "In Progress" {
+		t.Errorf("expected second column='In Progress', got %s", columns[1].Title)
+	}
+	if columns[2].Title != "Done" {
+		t.Errorf("expected third column='Done', got %s", columns[2].Title)
+	}
+}
+
+func TestClient_GetColumns_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")
+
+	columns, err := client.GetColumns(context.Background(), 1)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if len(columns) != 0 {
+		t.Errorf("expected 0 columns, got %d", len(columns))
+	}
+}
+
+func TestClient_GetColumn(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 != "getColumn" {
+			t.Errorf("expected method=getColumn, got %s", req.Method)
+		}
+
+		params := req.Params.(map[string]any)
+		if params["column_id"].(float64) != 5 {
+			t.Errorf("expected column_id=5, got %v", params["column_id"])
+		}
+
+		resp := JSONRPCResponse{
+			JSONRPC: "2.0",
+			ID:      req.ID,
+			Result:  json.RawMessage(`{"id": "5", "title": "Backlog", "position": "1", "project_id": "1", "task_limit": "10"}`),
+		}
+		json.NewEncoder(w).Encode(resp)
+	}))
+	defer server.Close()
+
+	client := NewClient(server.URL).WithAPIToken("test-token")
+
+	column, err := client.GetColumn(context.Background(), 5)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if int(column.ID) != 5 {
+		t.Errorf("expected ID=5, got %d", column.ID)
+	}
+	if column.Title != "Backlog" {
+		t.Errorf("expected title='Backlog', got %s", column.Title)
+	}
+	if int(column.TaskLimit) != 10 {
+		t.Errorf("expected task_limit=10, got %d", column.TaskLimit)
+	}
+}
+
+func TestClient_GetColumn_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 columns
+		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.GetColumn(context.Background(), 999)
+	if err == nil {
+		t.Fatal("expected error for non-existent column")
+	}
+
+	if !errors.Is(err, ErrColumnNotFound) {
+		t.Errorf("expected ErrColumnNotFound, got %v", err)
+	}
+}
+
+func TestClient_GetColumns_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.GetColumns(ctx, 1)
+	if err == nil {
+		t.Fatal("expected error due to canceled context")
+	}
+}