test: runner loads Lua modules from system install #42582

cmake/RunTests.cmake

@@ -9,7 +9,7 @@ else()
 endif()
 
 set(ENV{NVIM_TEST} "1")
-# The runner's own Lua uses this runtime, not one installed under the install prefix.
+# Test runner should use the runtime from the build, not the system install (if any).
 set(ENV{VIMRUNTIME} ${ROOT_DIR}/runtime)
 # Set LC_ALL to meet expectations of some locale-sensitive tests.
 set(ENV{LC_ALL} "en_US.UTF-8")

test/run_tests.zig

@@ -21,6 +21,8 @@ pub fn testStep(b: *std.Build, kind: []const u8, nvim_bin: *std.Build.Step.Compi
 
     const env = test_step.getEnvMap();
     try env.put("NVIM_TEST", "1");
+    // Test runner should use the runtime from the build, not the system install (if any).
+    try env.put("VIMRUNTIME", try b.build_root.join(b.graph.arena, &.{"runtime"}));
     if (env.get("NVIM_LOG_FILE") == null) {
         try env.put("NVIM_LOG_FILE", b.fmt("{s}/nvim.log", .{b.install_path}));
     }