diff --git a/cmd/repl/repl_test.go b/cmd/repl/repl_test.go
index 414a2be..efd93dc 100644
--- a/cmd/repl/repl_test.go
+++ b/cmd/repl/repl_test.go
@@ -15,6 +15,9 @@
 package main
 
 import (
+	"errors"
+	"os"
+	"path/filepath"
 	"strings"
 	"testing"
 )
@@ -34,14 +37,14 @@ func TestValidateFlags(t *testing.T) {
 		},
 		{
 			name:            "cql file suffix is valid",
-			cqlInputText:    "/tmp/cql.cql",
+			cqlInputText:    filepath.Join("tmp", "cql.cql"),
 			bundleFileText:  "",
 			valuesetDirText: "",
 		},
 		{
 			name:            "bundle json suffix is valid",
 			cqlInputText:    "",
-			bundleFileText:  "/tmp/bundle.json",
+			bundleFileText:  filepath.Join("tmp", "bundle.json"),
 			valuesetDirText: "",
 		},
 		{
@@ -70,7 +73,7 @@ func TestValidateFlagsError(t *testing.T) {
 	}{
 		{
 			name:            "cql file without cql suffix returns error",
-			cqlInputText:    "/tmp/cql.txt",
+			cqlInputText:    filepath.Join("tmp", "cql.txt"),
 			bundleFileText:  "",
 			valuesetDirText: "",
 			wantErr:         "--cql_file flag is required to be a valid .cql",
@@ -78,7 +81,7 @@ func TestValidateFlagsError(t *testing.T) {
 		{
 			name:            "bundle json file without json suffix returns error",
 			cqlInputText:    "",
-			bundleFileText:  "/tmp/bundle.txt",
+			bundleFileText:  filepath.Join("tmp", "bundle.txt"),
 			valuesetDirText: "",
 			wantErr:         "--bundle_file when specified, is required to be a valid json file",
 		},
@@ -86,7 +89,7 @@ func TestValidateFlagsError(t *testing.T) {
 			name:            "invalid directory returns error",
 			cqlInputText:    "",
 			bundleFileText:  "",
-			valuesetDirText: "/my/fake/dir",
+			valuesetDirText: filepath.Join("my", "fake", "dir"),
 			wantErr:         "no such file or directory",
 		},
 	}
@@ -98,3 +101,30 @@ func TestValidateFlagsError(t *testing.T) {
 		})
 	}
 }
+
+func TestValidateFlagPathError(t *testing.T) {
+	// Path errors can return different text for windows and linux, so we need to assert on the error
+	// itself, not the error text.
+	tests := []struct {
+		name            string
+		cqlInputText    string
+		bundleFileText  string
+		valuesetDirText string
+		wantErr         error
+	}{
+		{
+			name:            "invalid directory returns not exist error",
+			cqlInputText:    "",
+			bundleFileText:  "",
+			valuesetDirText: filepath.Join("my", "fake", "dir"),
+			wantErr:         os.ErrNotExist,
+		},
+	}
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			if err := validateFlags(tc.cqlInputText, tc.bundleFileText, tc.valuesetDirText); !errors.Is(err, tc.wantErr) {
+				t.Errorf("validateFlags() returned unexpected error (-want +got):\n%s, %s", tc.wantErr, err.Error())
+			}
+		})
+	}
+}
diff --git a/internal/iohelpers/files_test.go b/internal/iohelpers/files_test.go
index be5efc8..78eb93a 100644
--- a/internal/iohelpers/files_test.go
+++ b/internal/iohelpers/files_test.go
@@ -208,9 +208,11 @@ func TestWriteFileGCS(t *testing.T) {
 	}
 }
 
+// gcsPath returns the full GCS path for a given suffixPath.
+// Since these are not real file paths, we don't need to use filepath.Join.
 func gcsPath(t *testing.T, suffixPath string) string {
 	t.Helper()
-	return "gs://" + filepath.Join(testBucketName, suffixPath)
+	return "gs://" + testBucketName + "/" + suffixPath
 }
 
 func gcsObject(t *testing.T, content string) testhelpers.GCSObjectEntry {