[UT][WATERMARK] add gvawatermark display config parsing and behavioral tests

Add GStreamer Check tests for displ-cfg acceptance (all 10 config
keys), behavioral verification (show-labels toggles text rendering,
thickness scales pixel count, show-roi/hide-roi filter ROIs), edge
cases (show-roi+hide-roi conflict where show-roi wins, invalid config
value triggers pipeline error, multiple ROIs produce more pixels), and
a design-revealing test (show-labels=false silently disables show-roi
parsing due to nesting in parse_displ_config).

Not tested: font-scale/font-type/draw-txt-bg/text-x/text-y pixel-level
behavioral verification, tensor-driven rendering (landmarks, masks,
keypoints, OBB), displ-avgfps integration, VA/GPU render path.

Signed-off-by: Walid <walid.aly@intel.com>

Author: walidbarakat

tests/unit_tests/check/elements/CMakeLists.txt

@@ -1,5 +1,5 @@
 # ==============================================================================
-# Copyright (C) 2018-2025 Intel Corporation
+# Copyright (C) 2018-2026 Intel Corporation
 #
 # SPDX-License-Identifier: MIT
 # ==============================================================================
@@ -10,6 +10,7 @@ add_subdirectory(classification)
 add_subdirectory(metaconvert)
 add_subdirectory(metapublish)
 add_subdirectory(fpscounter)
+add_subdirectory(watermark)
 add_subdirectory(properties)
 
 if(${ENABLE_AUDIO_INFERENCE_ELEMENTS})

tests/unit_tests/check/elements/watermark/CMakeLists.txt

@@ -0,0 +1,7 @@
+# ==============================================================================
+# Copyright (C) 2026 Intel Corporation
+#
+# SPDX-License-Identifier: MIT
+# ==============================================================================
+
+add_subdirectory(test_watermark)

tests/unit_tests/check/elements/watermark/test_watermark/CMakeLists.txt

@@ -0,0 +1,13 @@
+# ==============================================================================
+# Copyright (C) 2026 Intel Corporation
+#
+# SPDX-License-Identifier: MIT
+# ==============================================================================
+
+set(COMMON_LIBS test_common test_utils)
+
+# --- Display config parsing tests ---
+set(TARGET_CONFIG "test_gvawatermark_config")
+add_executable(${TARGET_CONFIG} ${CMAKE_CURRENT_SOURCE_DIR}/test_watermark_config.cpp)
+target_link_libraries(${TARGET_CONFIG} PRIVATE ${COMMON_LIBS})
+add_test(NAME ${TARGET_CONFIG} COMMAND ${TARGET_CONFIG} WORKING_DIRECTORY ${CMAKE_RUNTIME_OUTPUT_DIRECTORY})