diff --git a/NEWS.md b/NEWS.md
index a25451d5..3783ee32 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,5 +1,6 @@
 # bayesplot (development version)
 
+* Added unit tests for previously untested edge cases in `param_range()`, `param_glue()`, and `tidyselect_parameters()` (no-match, partial-match, and negation behavior).
 * Bumped minimum version for `rstantools` from `>= 1.5.0` to `>= 2.0.0` .
 * Use `rlang::warn()` and `rlang::inform()` for selected PPC user messages instead of base `warning()` and `message()`.
 * Standardize input validation errors in `ppc_km_overlay()` and interpolation helpers to use `rlang::abort()` for consistent error handling.
diff --git a/tests/testthat/test-tidy-params.R b/tests/testthat/test-tidy-params.R
new file mode 100644
index 00000000..5a8b62d5
--- /dev/null
+++ b/tests/testthat/test-tidy-params.R
@@ -0,0 +1,40 @@
+source(test_path("data-for-mcmc-tests.R"))
+
+# param_range --------------------------------------------------------------
+
+test_that("param_range returns empty integer when no matches", {
+  all_pars <- c("alpha", "gamma[1]", "gamma[2]")
+  result <- param_range("beta", 1:3, vars = all_pars)
+  expect_identical(result, integer(0))
+})
+
+test_that("param_range drops non-matching indices silently", {
+  all_pars <- c("alpha", "beta[1]", "beta[3]")
+  # beta[2] does not exist, should be silently dropped
+  result <- param_range("beta", 1:3, vars = all_pars)
+  expect_equal(result, c(2L, 3L))
+})
+
+# param_glue ---------------------------------------------------------------
+
+test_that("param_glue returns empty integer when no matches", {
+  all_pars <- c("alpha", "sigma")
+  result <- param_glue("beta[{i}]", i = 1:3, vars = all_pars)
+  expect_identical(result, integer(0))
+})
+
+test_that("param_glue drops non-matching names silently", {
+  all_pars <- c("b[X:1]", "b[Y:2]", "sigma")
+  # b[X:2] and b[Y:1] don't exist
+  result <- param_glue("b[{var}:{lev}]", var = c("X", "Y"), lev = c(1, 2),
+                       vars = all_pars)
+  expect_equal(result, c(1L, 2L))
+})
+
+# tidyselect_parameters ----------------------------------------------------
+
+test_that("tidyselect_parameters works with negation", {
+  all_pars <- c("alpha", "beta[1]", "beta[2]", "sigma")
+  selected <- tidyselect_parameters(all_pars, vars(-alpha))
+  expect_equal(selected, c("beta[1]", "beta[2]", "sigma"))
+})