diff --git a/src/tools/tidy/src/allowed_run_make_makefiles.txt b/src/tools/tidy/src/allowed_run_make_makefiles.txt
index 14f0a9cd23d21..96ab097b3885e 100644
--- a/src/tools/tidy/src/allowed_run_make_makefiles.txt
+++ b/src/tools/tidy/src/allowed_run_make_makefiles.txt
@@ -9,7 +9,6 @@ run-make/incr-add-rust-src-component/Makefile
 run-make/issue-84395-lto-embed-bitcode/Makefile
 run-make/jobserver-error/Makefile
 run-make/libs-through-symlinks/Makefile
-run-make/libtest-json/Makefile
 run-make/libtest-junit/Makefile
 run-make/libtest-thread-limit/Makefile
 run-make/macos-deployment-target/Makefile
diff --git a/tests/run-make/libtest-json/Makefile b/tests/run-make/libtest-json/Makefile
deleted file mode 100644
index c8bc7b5dd4a4c..0000000000000
--- a/tests/run-make/libtest-json/Makefile
+++ /dev/null
@@ -1,20 +0,0 @@
-# ignore-cross-compile
-# needs-unwind
-include ../tools.mk
-
-# Test expected libtest's JSON output
-
-OUTPUT_FILE_DEFAULT := $(TMPDIR)/libtest-json-output-default.json
-OUTPUT_FILE_STDOUT_SUCCESS := $(TMPDIR)/libtest-json-output-stdout-success.json
-
-all: f.rs validate_json.py output-default.json output-stdout-success.json
-	$(RUSTC) --test f.rs
-	RUST_BACKTRACE=0 $(call RUN,f) -Z unstable-options --test-threads=1 --format=json > $(OUTPUT_FILE_DEFAULT) || true
-	RUST_BACKTRACE=0 $(call RUN,f) -Z unstable-options --test-threads=1 --format=json --show-output > $(OUTPUT_FILE_STDOUT_SUCCESS) || true
-
-	cat $(OUTPUT_FILE_DEFAULT) | "$(PYTHON)" validate_json.py
-	cat $(OUTPUT_FILE_STDOUT_SUCCESS) | "$(PYTHON)" validate_json.py
-
-	# Normalize the actual output and compare to expected output file
-	cat $(OUTPUT_FILE_DEFAULT) | sed 's/"exec_time": [0-9.]*/"exec_time": $$TIME/' | diff output-default.json -
-	cat $(OUTPUT_FILE_STDOUT_SUCCESS) | sed 's/"exec_time": [0-9.]*/"exec_time": $$TIME/' | diff output-stdout-success.json -
diff --git a/tests/run-make/libtest-json/output-default.json b/tests/run-make/libtest-json/output-default.json
index 01710f59e5d74..a2293a032d012 100644
--- a/tests/run-make/libtest-json/output-default.json
+++ b/tests/run-make/libtest-json/output-default.json
@@ -7,4 +7,4 @@
 { "type": "test", "name": "c", "event": "ok" }
 { "type": "test", "event": "started", "name": "d" }
 { "type": "test", "name": "d", "event": "ignored", "message": "msg" }
-{ "type": "suite", "event": "failed", "passed": 2, "failed": 1, "ignored": 1, "measured": 0, "filtered_out": 0, "exec_time": $TIME }
+{ "type": "suite", "event": "failed", "passed": 2, "failed": 1, "ignored": 1, "measured": 0, "filtered_out": 0, "exec_time": "$EXEC_TIME" }
diff --git a/tests/run-make/libtest-json/output-stdout-success.json b/tests/run-make/libtest-json/output-stdout-success.json
index 878eb6c7c260d..cf92f01f63aca 100644
--- a/tests/run-make/libtest-json/output-stdout-success.json
+++ b/tests/run-make/libtest-json/output-stdout-success.json
@@ -7,4 +7,4 @@
 { "type": "test", "name": "c", "event": "ok", "stdout": "thread 'c' panicked at f.rs:15:5:\nassertion failed: false\n" }
 { "type": "test", "event": "started", "name": "d" }
 { "type": "test", "name": "d", "event": "ignored", "message": "msg" }
-{ "type": "suite", "event": "failed", "passed": 2, "failed": 1, "ignored": 1, "measured": 0, "filtered_out": 0, "exec_time": $TIME }
+{ "type": "suite", "event": "failed", "passed": 2, "failed": 1, "ignored": 1, "measured": 0, "filtered_out": 0, "exec_time": "$EXEC_TIME" }
diff --git a/tests/run-make/libtest-json/rmake.rs b/tests/run-make/libtest-json/rmake.rs
new file mode 100644
index 0000000000000..acbd88dc46cb9
--- /dev/null
+++ b/tests/run-make/libtest-json/rmake.rs
@@ -0,0 +1,31 @@
+// Check libtest's JSON output against snapshots.
+
+//@ ignore-cross-compile
+//@ needs-unwind (test file contains #[should_panic] test)
+
+use run_make_support::{cmd, diff, python_command, rustc};
+
+fn main() {
+    rustc().arg("--test").input("f.rs").run();
+
+    run_tests(&[], "output-default.json");
+    run_tests(&["--show-output"], "output-stdout-success.json");
+}
+
+#[track_caller]
+fn run_tests(extra_args: &[&str], expected_file: &str) {
+    let cmd_out = cmd("./f")
+        .env("RUST_BACKTRACE", "0")
+        .args(&["-Zunstable-options", "--test-threads=1", "--format=json"])
+        .args(extra_args)
+        .run_fail();
+    let test_stdout = &cmd_out.stdout_utf8();
+
+    python_command().arg("validate_json.py").stdin(test_stdout).run();
+
+    diff()
+        .expected_file(expected_file)
+        .actual_text("stdout", test_stdout)
+        .normalize(r#"(?<prefix>"exec_time": )[0-9.]+"#, r#"${prefix}"$$EXEC_TIME""#)
+        .run();
+}