feat(rules): add Go testing standards

.cursor/rules/go.mdc

@@ -57,6 +57,20 @@ When working with Go:
      - `gorm:"index"` for indexed fields
      - `gorm:"type:text"` for specific SQL types
 
+7. Testing Standards:
+   - Place tests in _test.go files next to the code they test
+   - Use table-driven tests for multiple test cases
+   - Use meaningful test names that describe the scenario
+   - Create test helpers for common setup/teardown
+   - Use subtests for related test cases
+   - Test both success and error cases
+   - For database tests:
+     - Use in-memory SQLite for speed
+     - Clean up after each test
+     - Use transactions where appropriate
+   - Write focused tests that test one thing
+   - Include examples in test files when helpful
+
 metadata:
   priority: high
   version: 1.0
@@ -98,4 +112,31 @@ examples:
       # Good: GORM query building and error handling
       if err := db.Model(&Note{}).Where("id = ?", id).Update("content", content).Error; err != nil {
           return fmt.Errorf("failed to update note: %w", err)
+      }
+
+  - input: |
+      # Bad: Single monolithic test
+      func TestFeature(t *testing.T) {
+          // Test everything here
+      }
+    output: |
+      # Good: Table-driven tests with subtests
+      func TestFeature(t *testing.T) {
+          tests := []struct{
+              name string
+              input string
+              want string
+          }{
+              {"simple case", "input", "want"},
+              {"edge case", "edge", "result"},
+          }
+          
+          for _, tt := range tests {
+              t.Run(tt.name, func(t *testing.T) {
+                  got := Feature(tt.input)
+                  if got != tt.want {
+                      t.Errorf("got %v, want %v", got, tt.want)
+                  }
+              })
+          }
       }