tests: add bridge networking test

Add test_multiple_containers_same_internal_port() to verify the key
benefit of bridge networking: multiple containers can listen on the
same internal port with different host port mappings.

The test runs two nginx containers both listening on port 80 internally,
mapped to host ports 8080 and 8081, and verifies both are accessible.

Also update TestPortForwarding docstring to reflect the change from
host networking to bridge networking.

Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>

1 files changed, 70 insertions, 2 deletions

diff --git a/tests/test_vdkr.py b/tests/test_vdkr.py
index 81715d16..c343e05f 100644
--- a/tests/test_vdkr.py
+++ b/tests/test_vdkr.py
@@ -80,8 +80,9 @@ class TestPortForwarding:
     """Test port forwarding with memres.
 
     Port forwarding allows access to services running in containers from the host.
-    --network=host is used by default for all containers since Docker bridge
-    networking is not available inside the QEMU VM.
+    Docker bridge networking (docker0, 172.17.0.0/16) is used by default.
+    Each container gets its own IP, enabling multiple containers to listen
+    on the same internal port with different host port mappings.
     """
 
     @pytest.mark.network
@@ -135,6 +136,73 @@ class TestPortForwarding:
             # Stop memres
             vdkr.memres_stop()
 
+    @pytest.mark.network
+    @pytest.mark.slow
+    def test_multiple_containers_same_internal_port(self, vdkr):
+        """Test multiple containers listening on same internal port.
+
+        This tests the key benefit of bridge networking:
+        - nginx1 listens on container port 80, mapped to host port 8080
+        - nginx2 listens on container port 80, mapped to host port 8081
+        - Both should work simultaneously (impossible with --network=host)
+        """
+        import subprocess
+        import time
+
+        # Stop any running memres first
+        vdkr.memres_stop()
+
+        # Start memres
+        result = vdkr.memres_start(timeout=180)
+        assert result.returncode == 0, f"memres start failed: {result.stderr}"
+
+        try:
+            # Pull nginx:alpine if not present
+            vdkr.run("pull", "nginx:alpine", timeout=300)
+
+            # Run first nginx on host:8080 -> container:80
+            result1 = vdkr.run("run", "-d", "--name", "nginx1", "-p", "8080:80",
+                               "nginx:alpine", timeout=60)
+            assert result1.returncode == 0, f"nginx1 run failed: {result1.stderr}"
+
+            # Run second nginx on host:8081 -> container:80 (same internal port!)
+            result2 = vdkr.run("run", "-d", "--name", "nginx2", "-p", "8081:80",
+                               "nginx:alpine", timeout=60)
+            assert result2.returncode == 0, f"nginx2 run failed: {result2.stderr}"
+
+            # Give nginx time to start
+            time.sleep(3)
+
+            # Test both are accessible
+            curl1 = subprocess.run(
+                ["curl", "-s", "-o", "/dev/null", "-w", "%{http_code}",
+                 "http://localhost:8080"],
+                capture_output=True, text=True, timeout=10
+            )
+            assert curl1.stdout == "200", f"nginx1: Expected HTTP 200, got {curl1.stdout}"
+
+            curl2 = subprocess.run(
+                ["curl", "-s", "-o", "/dev/null", "-w", "%{http_code}",
+                 "http://localhost:8081"],
+                capture_output=True, text=True, timeout=10
+            )
+            assert curl2.stdout == "200", f"nginx2: Expected HTTP 200, got {curl2.stdout}"
+
+            # Verify ps shows both containers with their port mappings
+            ps_result = vdkr.run("ps")
+            assert "nginx1" in ps_result.stdout
+            assert "nginx2" in ps_result.stdout
+            assert "8080" in ps_result.stdout
+            assert "8081" in ps_result.stdout
+
+        finally:
+            # Clean up
+            vdkr.run("stop", "nginx1", timeout=10, check=False)
+            vdkr.run("stop", "nginx2", timeout=10, check=False)
+            vdkr.run("rm", "-f", "nginx1", check=False)
+            vdkr.run("rm", "-f", "nginx2", check=False)
+            vdkr.memres_stop()
+
 
 class TestImages:
     """Test image management commands."""