Add test for handling pipeline error (#2547)

Credits: @langecode

Taken from #2504

server/api/helper_test.go

@@ -0,0 +1,41 @@
+package api
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+
+	"github.com/woodpecker-ci/woodpecker/server/pipeline"
+)
+
+func TestHandlePipelineError(t *testing.T) {
+	tests := []struct {
+		err  error
+		code int
+	}{
+		{
+			err:  pipeline.ErrFiltered,
+			code: http.StatusNoContent,
+		},
+		{
+			err:  &pipeline.ErrNotFound{Msg: "pipeline not found"},
+			code: http.StatusNotFound,
+		},
+		{
+			err:  &pipeline.ErrBadRequest{Msg: "bad request error"},
+			code: http.StatusBadRequest,
+		},
+	}
+
+	for _, tt := range tests {
+		r := httptest.NewRecorder()
+		c, _ := gin.CreateTestContext(r)
+		handlePipelineErr(c, tt.err)
+		c.Writer.WriteHeaderNow() // require written header
+		if r.Code != tt.code {
+			t.Errorf("status code: %d - expected: %d", r.Code, tt.code)
+		}
+	}
+}