3 files changed, 22 insertions, 4 deletions
diff --git a/lib/path/tests/default.nix b/lib/path/tests/default.nix
index 9a31e42828f48..6b8e515f43304 100644
--- a/lib/path/tests/default.nix
+++ b/lib/path/tests/default.nix
@@ -24,8 +24,9 @@ pkgs.runCommand "lib-path-tests" {
   export TEST_LIB=$PWD/lib
 
   echo "Running unit tests lib/path/tests/unit.nix"
-  nix-instantiate --eval lib/path/tests/unit.nix \
-    --argstr libpath "$TEST_LIB"
+  nix-instantiate --eval --show-trace \
+    --argstr libpath "$TEST_LIB" \
+    lib/path/tests/unit.nix
 
   echo "Running property tests lib/path/tests/prop.sh"
   bash lib/path/tests/prop.sh ${toString seed}
diff --git a/lib/path/tests/prop.sh b/lib/path/tests/prop.sh
index d6021cfcd5fe2..f321fdf1cf450 100755
--- a/lib/path/tests/prop.sh
+++ b/lib/path/tests/prop.sh
@@ -74,7 +74,7 @@ fi
 
 # Precalculate all normalisations with a single Nix call. Calling Nix for each
 # string individually would take way too long
-nix-instantiate --eval --strict --json \
+nix-instantiate --eval --strict --json --show-trace \
     --argstr libpath "$TEST_LIB" \
     --argstr dir "$tmp/strings" \
     "$SCRIPT_DIR"/prop.nix \
diff --git a/lib/path/tests/unit.nix b/lib/path/tests/unit.nix
index 61c4ab4d6f2ee..9c5b752cf64a3 100644
--- a/lib/path/tests/unit.nix
+++ b/lib/path/tests/unit.nix
@@ -3,7 +3,7 @@
 { libpath }:
 let
   lib = import libpath;
-  inherit (lib.path) append subpath;
+  inherit (lib.path) hasPrefix append subpath;
 
   cases = lib.runTests {
     # Test examples from the lib.path.append documentation
@@ -40,6 +40,23 @@ let
       expected = false;
     };
 
+    testHasPrefixExample1 = {
+      expr = hasPrefix /foo /foo/bar;
+      expected = true;
+    };
+    testHasPrefixExample2 = {
+      expr = hasPrefix /foo /foo;
+      expected = true;
+    };
+    testHasPrefixExample3 = {
+      expr = hasPrefix /foo/bar /foo;
+      expected = false;
+    };
+    testHasPrefixExample4 = {
+      expr = hasPrefix /. /foo;
+      expected = true;
+    };
+
     # Test examples from the lib.path.subpath.isValid documentation
     testSubpathIsValidExample1 = {
       expr = subpath.isValid null;