diff --git a/tests/builder.nix b/tests/builder.nix
index 8ab89053d..30c8c83b9 100644
--- a/tests/builder.nix
+++ b/tests/builder.nix
@@ -51,7 +51,11 @@ let
 
         mkdir -p $out/bin
         cp ${pname}.elf $out/bin
-        cp ${pname}.cover $out
+        if [ -f ${pname}.cover ]; then
+          cp ${pname}.cover $out/
+        else
+          echo "-assert *" > $out/${pname}.cover
+        fi
 
         ${jqBin} --null-input \
           --arg name ${pname} \
diff --git a/tests/mlir/default.nix b/tests/mlir/default.nix
index 0ce7161aa..f612b1fb7 100644
--- a/tests/mlir/default.nix
+++ b/tests/mlir/default.nix
@@ -55,11 +55,9 @@ let
           ${caseName}.c $pname.S ${t1main} \
           -o $pname.elf
 
-        if [ ! -f ${sourcePath}/${caseName}.json ]; then
-          echo "Error: ${sourcePath}/${caseName}.json not found" >&2
-        else
+        if [ -f "${sourcePath}/${caseName}.json" ]; then
           ${jq}/bin/jq -r '[.assert[] | "+assert " + .name] + [.tree[] | "+tree " + .name] + [.module[] | "+module " + .name] | .[]' \
-              ${sourcePath}/${caseName}.json > $pname.cover
+              "${sourcePath}/${caseName}.json" > $pname.cover
         fi
 
         runHook postBuild