Add issue proposal document for replacing go-github-mock with testify/mock

Co-authored-by: JoannaaKL <67866556+JoannaaKL@users.noreply.github.com>

Author: Copilot

docs/issues/replace-go-github-mock.md

@@ -0,0 +1,114 @@
+# Replace migueleliasweb/go-github-mock with stretchr/testify/mock
+
+**Type:** Enhancement / Refactoring  
+**Labels:** `enhancement`, `testing`, `technical-debt`
+
+---
+
+### Describe the feature or problem you'd like to solve
+
+The current test suite uses [migueleliasweb/go-github-mock](https://github.com/migueleliasweb/go-github-mock) for mocking GitHub REST API responses in unit tests. While this library has served us well, there are several reasons to consider replacing it with [stretchr/testify/mock](https://github.com/stretchr/testify):
+
+1. **Dependency Consolidation**: We already use `stretchr/testify` for assertions (`assert` and `require`). Using `testify/mock` would consolidate our testing dependencies.
+
+2. **Interface-based Mocking**: `testify/mock` encourages interface-based mocking, which leads to better separation of concerns and more flexible test design.
+
+3. **Maintenance & Activity**: `stretchr/testify` is one of the most widely used Go testing libraries with active maintenance.
+
+4. **Type Safety**: Interface-based mocking provides compile-time type checking, whereas HTTP-level mocking relies on runtime matching.
+
+5. **Test Clarity**: Mock expectations at the interface level make tests more readable and focused on behavior rather than HTTP transport details.
+
+### Current State
+
+The codebase currently uses `go-github-mock` extensively (metrics from `grep` search):
+
+| Metric | Count |
+|--------|-------|
+| Files using go-github-mock | 16 |
+| `mock.NewMockedHTTPClient` calls | ~449 |
+| `mock.WithRequestMatchHandler` calls | ~267 |
+| `mock.WithRequestMatch` calls | ~79 |
+| Unique mock endpoint patterns | ~80+ |
+
+*Note: Run `grep -c "mock.NewMockedHTTPClient" pkg/github/*_test.go` to verify current counts.*
+
+**Files affected:**
+- `pkg/github/*_test.go` (14 files)
+- `pkg/raw/raw_test.go`
+- `pkg/raw/raw_mock.go`
+
+### Proposed solution
+
+Replace HTTP-level mocking with interface-based mocking using `testify/mock`:
+
+#### Phase 1: Create Mock Interfaces
+1. Define interfaces for GitHub client operations (if not already present)
+2. Create mock implementations using `testify/mock`
+3. Update the codebase to depend on interfaces rather than concrete clients
+
+#### Phase 2: Migrate Tests Incrementally
+1. Start with a single test file to establish patterns
+2. Create helper functions for common mock setups
+3. Migrate remaining test files one at a time
+4. Remove `go-github-mock` dependency when complete
+
+#### Example Migration
+
+**Before (HTTP-level mocking):**
+```go
+mockedClient := mock.NewMockedHTTPClient(
+    mock.WithRequestMatch(
+        mock.GetReposIssuesByOwnerByRepoByIssueNumber,
+        mockIssue,
+    ),
+)
+client := github.NewClient(mockedClient)
+```
+
+**After (Interface-based mocking):**
+```go
+mockClient := new(MockGitHubClient)
+mockClient.On("GetIssue", ctx, "owner", "repo", 42).Return(mockIssue, nil)
+```
+
+### Benefits
+
+1. **Simpler Test Setup**: No need to construct HTTP responses
+2. **Better Error Testing**: Easy to mock error conditions without crafting HTTP error responses
+3. **Faster Tests**: No HTTP round-trip overhead (even if mocked)
+4. **Clearer Intent**: Tests read more like specifications
+5. **Reduced Dependencies**: One less external dependency to maintain
+
+### Considerations
+
+1. **Migration Effort**: This is a significant refactoring with ~449 mock usages to update
+2. **Interface Design**: Need to carefully design interfaces that balance granularity and usability
+3. **GraphQL Mocking**: The existing `githubv4mock` for GraphQL is **out of scope** for this issue and will remain unchanged. It already provides a different mocking approach specific to GraphQL.
+4. **Breaking Changes**: Test file changes only, no production code changes expected
+
+### Implementation Plan
+
+- [ ] Audit current mock usage patterns to identify common interfaces needed
+- [ ] Design and implement mock interfaces for GitHub REST API client
+- [ ] Create helper functions and test utilities for common mock scenarios
+- [ ] Migrate test files incrementally (suggest starting with smallest files):
+  - [ ] `pkg/github/code_scanning_test.go` (~4 mocks)
+  - [ ] `pkg/github/secret_scanning_test.go` (~5 mocks)
+  - [ ] `pkg/github/dependabot_test.go` (~6 mocks)
+  - [ ] Continue with remaining files...
+- [ ] Update `docs/testing.md` to reflect new mocking patterns
+- [ ] Remove `go-github-mock` from `go.mod` after complete migration
+
+### Additional context
+
+**Current testing documentation reference:**
+> Mocking is performed using [go-github-mock](https://github.com/migueleliasweb/go-github-mock) or `githubv4mock` for simulating GitHub REST and GQL API responses.
+
+This will need to be updated to:
+> Mocking is performed using [testify/mock](https://github.com/stretchr/testify#mock-package) for interface-based mocking or `githubv4mock` for simulating GitHub GQL API responses.
+
+### Related
+
+- [stretchr/testify documentation](https://pkg.go.dev/github.com/stretchr/testify/mock)
+- Current testing guidelines: [`docs/testing.md`](../testing.md)