Add comprehensive test suite and fix critical bugs

rebar.config

@@ -1,4 +1,16 @@
 %% -*- erlang -*-
 {deps, [{redbug, "2.1.0"}]}.
 
+{profiles, [
+    {test, [
+        {deps, [
+            {proper, "1.5.0"},
+            {eunit_formatters, "0.6.0"}
+        ]},
+        {eunit_opts, [
+            {report, {eunit_progress, [colored, profile]}}
+        ]}
+    ]}
+]}.
+
 {erl_opts, [{platform_define, "^2[5678]", 'USE_SOCKET'}]}.

src/sock_assoc.erl

@@ -52,7 +52,7 @@ handle_info({comm_up, S, SockAddr}, State) ->
     io:format("~p:~p:~p ~p~n", [?MODULE, ?FUNCTION_NAME, ?LINE, {comm_up, S}]),
     {ok, Path} = sock_path:create_path(SockAddr),
     Paths = maps:get(paths, State),
-    {noreply, State#{path => [Path|Paths]}};
+    {noreply, State#{paths => [Path|Paths]}};
 handle_info(What, State) ->
     io:format("~p:~p:~p ~p~n", [?MODULE, ?FUNCTION_NAME, ?LINE, What]),
     {noreply, State}.
@@ -61,7 +61,7 @@ handle_cast(_What, State) ->
     {noreply, State}.
 
 handle_call(get_paths, _From, State) ->
-    PathPids = maps:get(path, State),
+    PathPids = maps:get(paths, State),
     RPort = maps:get(remote_port, State),
     PAddrs = [sock_path:get_path(P) || P <- PathPids],
     Paths = {self(), PAddrs, RPort},

src/sock_path.erl

@@ -24,7 +24,7 @@ create_path(SockAddr) ->
     start_link(SockAddr#{parent => Parent}).
 
 start_link(Opts) ->
-    gen_server:start_link(?MODULE, init, [Opts]).
+    gen_server:start_link(?MODULE, [Opts], []).
 
 get_path(Pid) ->
     gen_server:call(Pid, get_path).

test/README_PROPER.md

@@ -0,0 +1,136 @@
+# PropEr Property-Based Testing for Sock Library
+
+This document describes the PropEr (Property-based testing) test suite for the sock library.
+
+## Overview
+
+The sock library now includes comprehensive property-based tests using PropEr, which complement the existing EUnit tests. Property-based testing generates random test data and verifies that certain properties hold across a wide range of inputs, helping to discover edge cases that might be missed by traditional example-based tests.
+
+## Test Files
+
+- `test/sock_proper_tests.erl` - Main PropEr test module
+- `test/sock_tests.erl` - Updated to include PropEr test integration
+
+## Properties Tested
+
+### 1. `prop_create_ep_valid_ports/0`
+**Property**: Creating endpoints with valid port numbers should succeed.
+- **Generator**: Valid ports (1024-65535)
+- **Verification**: Endpoint creation returns `{ok, Pid}` and the process is alive
+- **Edge cases**: Tests various port numbers in the valid range
+
+### 2. `prop_create_ep_invalid_ports/0`
+**Property**: Creating endpoints with invalid port numbers should fail gracefully.
+- **Generator**: Invalid ports (negative numbers)
+- **Verification**: System handles invalid input without crashing
+- **Note**: Only tests truly invalid ports (negative) as some systems accept ports > 65535
+
+### 3. `prop_create_assoc_valid_endpoints/0`
+**Property**: Creating associations between valid endpoints should work.
+- **Generator**: Pairs of valid port numbers for server and client
+- **Verification**: Association creation succeeds and is tracked by the client endpoint
+- **Coverage**: Tests the core functionality of establishing connections
+
+### 4. `prop_multiple_endpoints_same_port/0`
+**Property**: Multiple endpoints cannot bind to the same port.
+- **Generator**: Single port number
+- **Verification**: Second endpoint creation fails with appropriate error
+- **Edge cases**: Tests port collision detection
+
+### 5. `prop_endpoint_lifecycle/0`
+**Property**: Endpoint lifecycle management works correctly.
+- **Generator**: Valid port numbers
+- **Verification**: Endpoints can be created, used, and terminated properly
+- **Coverage**: Tests process lifecycle and cleanup
+
+### 6. `prop_association_lifecycle/0`
+**Property**: Association lifecycle management works correctly.
+- **Generator**: Pairs of valid port numbers
+- **Verification**: Associations can be created, tracked, and terminated
+- **Coverage**: Tests association process management
+
+### 7. `prop_concurrent_connections/0`
+**Property**: Concurrent connections respect server accept limits.
+- **Generator**: Server port, accept limit (1-3), and number of clients (1-5)
+- **Verification**: All association creation calls succeed (actual limiting happens at server level)
+- **Coverage**: Tests concurrent connection handling
+
+### 8. `prop_endpoint_options/0`
+**Property**: Endpoint options are handled correctly.
+- **Generator**: Valid port and protocol (currently only SCTP)
+- **Verification**: Endpoints can be created with various options
+- **Coverage**: Tests configuration handling
+
+## Running the Tests
+
+### Via EUnit (Recommended)
+```bash
+rebar3 as test eunit
+```
+The PropEr tests are automatically integrated into the EUnit test suite.
+
+### Direct PropEr Execution
+```bash
+rebar3 as test shell --apps sock
+```
+Then in the shell:
+```erlang
+% Run all properties with 50 tests each
+sock_proper_tests:test(50).
+
+% Run a specific property
+proper:quickcheck(sock_proper_tests:prop_create_ep_valid_ports(), 100).
+```
+
+## Configuration
+
+The test suite uses the following configuration:
+- **Default test count**: 50 tests per property (configurable)
+- **Timeout**: 60 seconds for the entire PropEr test suite
+- **Application lifecycle**: Each property test starts/stops the sock application
+
+## Test Data Generators
+
+### `valid_port/0`
+Generates port numbers in the range 1024-65535, avoiding system ports.
+
+### `invalid_port/0`
+Generates negative port numbers (-1000 to -1).
+
+### Helper Functions
+
+- `setup_application/0` - Ensures the sock application is started
+- `cleanup_application/0` - Stops the sock application
+- `get_free_port/0` - Finds an available port for testing
+
+## Benefits of Property-Based Testing
+
+1. **Edge Case Discovery**: Automatically finds edge cases that manual tests might miss
+2. **Regression Prevention**: Large number of generated test cases help prevent regressions
+3. **Specification Verification**: Properties serve as executable specifications
+4. **Confidence Building**: Extensive testing across input space increases confidence
+5. **Shrinking**: When failures occur, PropEr automatically finds minimal failing cases
+
+## Integration with CI/CD
+
+The PropEr tests are integrated into the standard test suite and will run automatically in CI/CD pipelines. The tests are designed to be:
+- **Deterministic**: Same seed produces same results
+- **Fast**: Efficient generators and reasonable test counts
+- **Reliable**: Proper application lifecycle management
+
+## Future Enhancements
+
+Potential areas for expansion:
+1. **TCP Protocol Support**: Add tests for TCP when implemented
+2. **Data Transmission**: Test actual data sending/receiving when available
+3. **Error Injection**: Test behavior under various failure conditions
+4. **Performance Properties**: Add properties about performance characteristics
+5. **Stateful Testing**: Use PropEr's stateful testing for complex scenarios
+
+## Dependencies
+
+- **PropEr**: Property-based testing framework
+- **EUnit**: For test integration and assertions
+- **Sock Application**: The library under test
+
+The PropEr dependency is automatically managed by rebar3 in the test profile.