diff --git a/deno.lock b/deno.lock
index 0770e57..85b9d84 100644
--- a/deno.lock
+++ b/deno.lock
@@ -1,16 +1,24 @@
 {
   "version": "5",
   "specifiers": {
+    "jsr:@std/assert@^1.0.13": "1.0.14",
     "jsr:@std/fmt@^1.0.8": "1.0.8",
     "jsr:@std/internal@^1.0.10": "1.0.12",
     "jsr:@std/path@^1.0.6": "1.1.2",
     "jsr:@std/semver@^1.0.3": "1.0.6",
+    "jsr:@std/testing@^1.0.3": "1.0.15",
     "jsr:@std/yaml@^1.0.5": "1.0.10",
     "npm:json5@^2.2.3": "2.2.3",
     "npm:jsonc-parser@^3.2.1": "3.3.1",
     "npm:yargs@^17.7.2": "17.7.2"
   },
   "jsr": {
+    "@std/assert@1.0.14": {
+      "integrity": "68d0d4a43b365abc927f45a9b85c639ea18a9fab96ad92281e493e4ed84abaa4",
+      "dependencies": [
+        "jsr:@std/internal"
+      ]
+    },
     "@std/fmt@1.0.8": {
       "integrity": "71e1fc498787e4434d213647a6e43e794af4fd393ef8f52062246e06f7e372b7"
     },
@@ -26,6 +34,13 @@
     "@std/semver@1.0.6": {
       "integrity": "b7c98ae2843547cf3f7ac37f3995889e6e4cee0a97b57b57f17f62722843303c"
     },
+    "@std/testing@1.0.15": {
+      "integrity": "a490169f5ccb0f3ae9c94fbc69d2cd43603f2cffb41713a85f99bbb0e3087cbc",
+      "dependencies": [
+        "jsr:@std/assert@^1.0.13",
+        "jsr:@std/internal"
+      ]
+    },
     "@std/yaml@1.0.10": {
       "integrity": "245706ea3511cc50c8c6d00339c23ea2ffa27bd2c7ea5445338f8feff31fa58e"
     }
diff --git a/src/hooks/patch.test.ts b/src/hooks/patch.test.ts
new file mode 100644
index 0000000..16a9a42
--- /dev/null
+++ b/src/hooks/patch.test.ts
@@ -0,0 +1,69 @@
+import { describe, it } from "testing/bdd";
+import { assertSpyCall, stub } from "testing/mock";
+import { parse } from "semver";
+import { patch } from "./patch.ts";
+
+describe("patch", () => {
+  it("should log formatted version string for csproj", async () => {
+    const consoleLogStub = stub(console, "log");
+    const readTextFileStub = stub(
+      Deno,
+      "readTextFile",
+      () =>
+        Promise.resolve(
+          "<Project>\n  <PropertyGroup>\n    <Version>1.0.0</Version>\n  </PropertyGroup>\n</Project>",
+        ),
+    );
+    const writeTextFileStub = stub(
+      Deno,
+      "writeTextFile",
+      () => Promise.resolve(),
+    );
+
+    try {
+      await patch("test.csproj", parse("1.2.3")!);
+
+      // Verify console.log was called with formatted string, not [object Object]
+      assertSpyCall(consoleLogStub, 0, {
+        args: ["patching 1.2.3 in test.csproj"],
+      });
+    } finally {
+      consoleLogStub.restore();
+      readTextFileStub.restore();
+      writeTextFileStub.restore();
+    }
+  });
+
+  it("should log formatted version string for package.json", async () => {
+    const consoleLogStub = stub(console, "log");
+    const readTextFileStub = stub(
+      Deno,
+      "readTextFile",
+      () => Promise.resolve('{"version": "1.0.0"}'),
+    );
+    const writeTextFileStub = stub(
+      Deno,
+      "writeTextFile",
+      () => Promise.resolve(),
+    );
+    const statStub = stub(
+      Deno,
+      "stat",
+      () => Promise.reject(new Deno.errors.NotFound()),
+    );
+
+    try {
+      await patch("package.json", parse("1.2.3")!);
+
+      // Verify console.log was called with formatted string, not [object Object]
+      assertSpyCall(consoleLogStub, 0, {
+        args: ["patching 1.2.3 in package.json"],
+      });
+    } finally {
+      consoleLogStub.restore();
+      readTextFileStub.restore();
+      writeTextFileStub.restore();
+      statStub.restore();
+    }
+  });
+});
diff --git a/src/hooks/replace.test.ts b/src/hooks/replace.test.ts
new file mode 100644
index 0000000..1434add
--- /dev/null
+++ b/src/hooks/replace.test.ts
@@ -0,0 +1,41 @@
+import { describe, it } from "testing/bdd";
+import { assertSpyCall, stub } from "testing/mock";
+import { parse } from "semver";
+import { replace } from "./replace.ts";
+
+describe("replace", () => {
+  it("should log formatted version strings", async () => {
+    const consoleLogStub = stub(console, "log");
+    const readTextFileStub = stub(
+      Deno,
+      "readTextFile",
+      () => Promise.resolve("version 1.0.0"),
+    );
+    const writeTextFileStub = stub(
+      Deno,
+      "writeTextFile",
+      () => Promise.resolve(),
+    );
+
+    try {
+      await replace("test.txt", parse("1.0.0")!, parse("1.2.3")!);
+
+      // Verify console.log was called with formatted strings, not [object Object]
+      assertSpyCall(consoleLogStub, 0, {
+        args: ["replacing 1.0.0 -> 1.2.3 in test.txt"],
+      });
+
+      // Verify file operations
+      assertSpyCall(readTextFileStub, 0, {
+        args: ["test.txt"],
+      });
+      assertSpyCall(writeTextFileStub, 0, {
+        args: ["test.txt", "version 1.2.3"],
+      });
+    } finally {
+      consoleLogStub.restore();
+      readTextFileStub.restore();
+      writeTextFileStub.restore();
+    }
+  });
+});
diff --git a/src/hooks/replace.ts b/src/hooks/replace.ts
index fb8819c..2e50e24 100644
--- a/src/hooks/replace.ts
+++ b/src/hooks/replace.ts
@@ -5,10 +5,10 @@ export async function replace(
   previous: SemVer,
   current: SemVer,
 ) {
-  console.log(`replacing ${previous} -> ${current} in ${file}`);
-  const contents = await Deno.readTextFile(file);
   const previousString = format(previous);
   const currentString = format(current);
+  console.log(`replacing ${previousString} -> ${currentString} in ${file}`);
+  const contents = await Deno.readTextFile(file);
   const updated = contents.replaceAll(previousString, currentString);
   await Deno.writeTextFile(file, updated);
 }