diff --git a/library/compiler-builtins/libm/crates/libm-test/src/lib.rs b/library/compiler-builtins/libm/crates/libm-test/src/lib.rs
index e3a690678416..eb457b0ae7bb 100644
--- a/library/compiler-builtins/libm/crates/libm-test/src/lib.rs
+++ b/library/compiler-builtins/libm/crates/libm-test/src/lib.rs
@@ -8,6 +8,7 @@ pub mod mpfloat;
 mod num;
 pub mod op;
 mod precision;
+mod run_cfg;
 mod test_traits;
 
 pub use f8_impl::f8;
@@ -15,7 +16,8 @@ pub use libm::support::{Float, Int, IntTy, MinInt};
 pub use num::{FloatExt, logspace};
 pub use op::{BaseName, FloatTy, Identifier, MathOp, OpCFn, OpFTy, OpRustFn, OpRustRet, Ty};
 pub use precision::{MaybeOverride, SpecialCase, default_ulp};
-pub use test_traits::{CheckBasis, CheckCtx, CheckOutput, GenerateInput, Hex, TupleCall};
+pub use run_cfg::{CheckBasis, CheckCtx};
+pub use test_traits::{CheckOutput, GenerateInput, Hex, TupleCall};
 
 /// Result type for tests is usually from `anyhow`. Most times there is no success value to
 /// propagate.
diff --git a/library/compiler-builtins/libm/crates/libm-test/src/run_cfg.rs b/library/compiler-builtins/libm/crates/libm-test/src/run_cfg.rs
new file mode 100644
index 000000000000..eb7e0e2c1a94
--- /dev/null
+++ b/library/compiler-builtins/libm/crates/libm-test/src/run_cfg.rs
@@ -0,0 +1,51 @@
+//! Configuration for how tests get run.
+
+#![allow(unused)]
+
+use std::collections::BTreeMap;
+use std::env;
+use std::sync::LazyLock;
+
+use crate::{BaseName, FloatTy, Identifier, op};
+
+pub const EXTENSIVE_ENV: &str = "LIBM_EXTENSIVE_TESTS";
+
+/// Context passed to [`CheckOutput`].
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub struct CheckCtx {
+    /// Allowed ULP deviation
+    pub ulp: u32,
+    pub fn_ident: Identifier,
+    pub base_name: BaseName,
+    /// Function name.
+    pub fn_name: &'static str,
+    /// Return the unsuffixed version of the function name.
+    pub base_name_str: &'static str,
+    /// Source of truth for tests.
+    pub basis: CheckBasis,
+}
+
+impl CheckCtx {
+    /// Create a new check context, using the default ULP for the function.
+    pub fn new(fn_ident: Identifier, basis: CheckBasis) -> Self {
+        let mut ret = Self {
+            ulp: 0,
+            fn_ident,
+            fn_name: fn_ident.as_str(),
+            base_name: fn_ident.base_name(),
+            base_name_str: fn_ident.base_name().as_str(),
+            basis,
+        };
+        ret.ulp = crate::default_ulp(&ret);
+        ret
+    }
+}
+
+/// Possible items to test against
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum CheckBasis {
+    /// Check against Musl's math sources.
+    Musl,
+    /// Check against infinite precision (MPFR).
+    Mpfr,
+}
diff --git a/library/compiler-builtins/libm/crates/libm-test/src/test_traits.rs b/library/compiler-builtins/libm/crates/libm-test/src/test_traits.rs
index ca933bbda63e..6b833dfb5ddb 100644
--- a/library/compiler-builtins/libm/crates/libm-test/src/test_traits.rs
+++ b/library/compiler-builtins/libm/crates/libm-test/src/test_traits.rs
@@ -11,44 +11,7 @@ use std::fmt;
 
 use anyhow::{Context, bail, ensure};
 
-use crate::{BaseName, Float, Identifier, Int, MaybeOverride, SpecialCase, TestResult};
-
-/// Context passed to [`CheckOutput`].
-#[derive(Clone, Debug, PartialEq, Eq)]
-pub struct CheckCtx {
-    /// Allowed ULP deviation
-    pub ulp: u32,
-    pub fn_ident: Identifier,
-    pub base_name: BaseName,
-    /// Function name.
-    pub fn_name: &'static str,
-    /// Source of truth for tests.
-    pub basis: CheckBasis,
-}
-
-impl CheckCtx {
-    /// Create a new check context, using the default ULP for the function.
-    pub fn new(fn_ident: Identifier, basis: CheckBasis) -> Self {
-        let mut ret = Self {
-            ulp: 0,
-            fn_ident,
-            fn_name: fn_ident.as_str(),
-            base_name: fn_ident.base_name(),
-            basis,
-        };
-        ret.ulp = crate::default_ulp(&ret);
-        ret
-    }
-}
-
-/// Possible items to test against
-#[derive(Clone, Debug, PartialEq, Eq)]
-pub enum CheckBasis {
-    /// Check against Musl's math sources.
-    Musl,
-    /// Check against infinite precision (MPFR).
-    Mpfr,
-}
+use crate::{CheckCtx, Float, Int, MaybeOverride, SpecialCase, TestResult};
 
 /// Implement this on types that can generate a sequence of tuples for test input.
 pub trait GenerateInput<TupleArgs> {