diff --git a/.github/package-lock.json b/.github/package-lock.json
index 5b2c8caf1214..0cc7db3ac3ae 100644
--- a/.github/package-lock.json
+++ b/.github/package-lock.json
@@ -2850,9 +2850,9 @@
       }
     },
     "node_modules/globals": {
-      "version": "17.2.0",
-      "resolved": "https://registry.npmjs.org/globals/-/globals-17.2.0.tgz",
-      "integrity": "sha512-tovnCz/fEq+Ripoq+p/gN1u7l6A7wwkoBT9pRCzTHzsD/LvADIzXZdjmRymh5Ztf0DYC3Rwg5cZRYjxzBmzbWg==",
+      "version": "17.3.0",
+      "resolved": "https://registry.npmjs.org/globals/-/globals-17.3.0.tgz",
+      "integrity": "sha512-yMqGUQVVCkD4tqjOJf3TnrvaaHDMYp4VlUSObbkIiuCPe/ofdMBFIAcBbCSRFWOnos6qRiTVStDwqPLUclaxIw==",
       "dev": true,
       "license": "MIT",
       "engines": {
diff --git a/.github/shared/package-lock.json b/.github/shared/package-lock.json
index 7277096f3c59..c16a5723ffdf 100644
--- a/.github/shared/package-lock.json
+++ b/.github/shared/package-lock.json
@@ -2224,9 +2224,9 @@
       }
     },
     "node_modules/globals": {
-      "version": "17.2.0",
-      "resolved": "https://registry.npmjs.org/globals/-/globals-17.2.0.tgz",
-      "integrity": "sha512-tovnCz/fEq+Ripoq+p/gN1u7l6A7wwkoBT9pRCzTHzsD/LvADIzXZdjmRymh5Ztf0DYC3Rwg5cZRYjxzBmzbWg==",
+      "version": "17.3.0",
+      "resolved": "https://registry.npmjs.org/globals/-/globals-17.3.0.tgz",
+      "integrity": "sha512-yMqGUQVVCkD4tqjOJf3TnrvaaHDMYp4VlUSObbkIiuCPe/ofdMBFIAcBbCSRFWOnos6qRiTVStDwqPLUclaxIw==",
       "dev": true,
       "license": "MIT",
       "engines": {
diff --git a/eng/common/scripts/login-to-github.ps1 b/eng/common/scripts/login-to-github.ps1
index 96023d290c4b..e911f31eb12b 100644
--- a/eng/common/scripts/login-to-github.ps1
+++ b/eng/common/scripts/login-to-github.ps1
@@ -57,9 +57,17 @@ function New-GitHubAppJwt {
     [Parameter(Mandatory)] [string] $AppId
   )
 
-  function Base64UrlEncode($json) {
-    $bytes = [System.Text.Encoding]::UTF8.GetBytes($json)
-    $base64 = [Convert]::ToBase64String($bytes)
+  function Base64UrlEncode {
+    param(
+      [string]$Data,
+      [switch]$IsBase64String
+    )
+    if ($IsBase64String) {
+      $base64 = $Data
+    } else {
+      $bytes = [System.Text.Encoding]::UTF8.GetBytes($Data)
+      $base64 = [Convert]::ToBase64String($bytes)
+    }
     return $base64.TrimEnd('=') -replace '\+', '-' -replace '/', '_'
   }
 
@@ -70,7 +78,7 @@ function New-GitHubAppJwt {
   }
   $Now = [int][double]::Parse((Get-Date -UFormat %s))
   $Payload = @{
-      iat = $Now
+      iat = $Now - 10 # 10 seconds clock skew
       exp = $Now + 600  # 10 minutes
       iss = $AppId
   }
@@ -97,7 +105,7 @@ function New-GitHubAppJwt {
     throw "Azure Key Vault response does not contain a signature. Response: $($SignResultJson | ConvertTo-Json -Compress)"
   }
 
-  $Signature = $SignResultJson.signature
+  $Signature = Base64UrlEncode -Data $SignResultJson.signature -IsBase64String
   return "$UnsignedToken.$Signature"
 }
 
diff --git a/eng/tools/openapi-diff-runner/package.json b/eng/tools/openapi-diff-runner/package.json
index 1096a5db64fd..167777b0270b 100644
--- a/eng/tools/openapi-diff-runner/package.json
+++ b/eng/tools/openapi-diff-runner/package.json
@@ -12,7 +12,7 @@
     "format:check": "prettier . --ignore-path ../.prettierignore --check",
     "format:check:ci": "prettier . --ignore-path ../.prettierignore --check --log-level debug",
     "test": "vitest",
-    "test:ci": "vitest --coverage --reporter=verbose"
+    "test:ci": "vitest run --coverage --reporter=verbose"
   },
   "engines": {
     "node": ">=20.0.0"
diff --git a/eng/tools/openapi-diff-runner/test/commands.test.ts b/eng/tools/openapi-diff-runner/test/commands.test.ts
new file mode 100644
index 000000000000..87fcb98e98bd
--- /dev/null
+++ b/eng/tools/openapi-diff-runner/test/commands.test.ts
@@ -0,0 +1,416 @@
+import { BREAKING_CHANGES_CHECK_TYPES } from "@azure-tools/specs-shared/breaking-change";
+import { getChangedFilesStatuses } from "@azure-tools/specs-shared/changed-files";
+import { devNull } from "node:os";
+import path, { resolve } from "node:path";
+import { fileURLToPath } from "node:url";
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import { createDummySwagger } from "../src/command-helpers.js";
+import { validateBreakingChange } from "../src/commands.js";
+import { runOad } from "../src/run-oad.js";
+
+const serviceParent = "specification/foo/data-plane/";
+
+vi.mock("@azure-tools/specs-shared/changed-files", async () => {
+  const actual = await vi.importActual("@azure-tools/specs-shared/changed-files");
+  return {
+    ...actual,
+    getChangedFilesStatuses: vi.fn(),
+  };
+});
+
+vi.mock("../src/run-oad.js", () => ({
+  runOad: vi.fn(),
+}));
+
+vi.mock("../src/command-helpers.js", async () => {
+  const actual = await vi.importActual("../src/command-helpers.js");
+  return {
+    ...actual,
+    createDummySwagger: vi.fn(),
+  };
+});
+
+function mockChangedFilesStatuses(
+  partial: Partial<{
+    additions: string[];
+    modifications: string[];
+    deletions: string[];
+    renames: { from: string; to: string }[];
+  }> = {},
+) {
+  const defaultResult = {
+    additions: [],
+    modifications: [],
+    deletions: [],
+    renames: [],
+    total: 0,
+  };
+
+  const result = { ...defaultResult, ...partial };
+
+  result.total =
+    result.additions.length +
+    result.modifications.length +
+    result.deletions.length +
+    result.renames.length;
+
+  return vi.mocked(getChangedFilesStatuses).mockResolvedValue(result);
+}
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+
+const context = {
+  localSpecRepoPath: "",
+  workingFolder: "",
+  logFileFolder: "",
+  swaggerDirs: [],
+  baseBranch: "",
+  headCommit: "",
+  runType: "",
+  checkName: "",
+  targetRepo: "",
+  sourceRepo: "",
+  prInfo: {
+    targetBranch: "",
+    sourceBranch: "",
+    baseBranch: "",
+    currentBranch: "",
+    tempRepoFolder: path.resolve(__dirname, "fixtures"),
+    checkout: function (branch: string): Promise<void> {
+      console.log("checkout " + branch);
+      return Promise.resolve();
+    },
+  },
+  prNumber: "",
+  prSourceBranch: "",
+  prTargetBranch: "",
+  oadMessageProcessorContext: {
+    logFilePath: devNull,
+    prUrl: "",
+    messageCache: [],
+  },
+  prUrl: "",
+};
+
+type TestCase = {
+  name: string;
+  changedFiles: {
+    additions?: string[];
+    modifications?: string[];
+    deletions?: string[];
+    renames?: {
+      from: string;
+      to: string;
+    }[];
+  };
+  expectedCreateDummySwaggers: { old: string[]; new: string[] };
+  expectedOadCalls: {
+    sameVersion: { old: string; new: string }[];
+    crossVersion: { old: string; new: string }[];
+  };
+};
+
+const cases: TestCase[] = [
+  {
+    name: "modify one file, one version",
+    changedFiles: {
+      modifications: ["Foo/stable/2025-03-01/foo.json"],
+    },
+    expectedCreateDummySwaggers: {
+      old: [],
+      new: [],
+    },
+    expectedOadCalls: {
+      sameVersion: [
+        {
+          old: "Foo/stable/2025-03-01/foo.json",
+          new: "Foo/stable/2025-03-01/foo.json",
+        },
+      ],
+      crossVersion: [],
+    },
+  },
+  {
+    name: "modify one file, multiple versions",
+    changedFiles: {
+      modifications: [
+        "Foo/preview/2025-04-01-preview/foo.json",
+        "Foo/stable/2025-01-01/foo.json",
+        "Foo/stable/2025-03-01/foo.json",
+      ],
+    },
+    expectedCreateDummySwaggers: {
+      old: [],
+      new: [],
+    },
+    expectedOadCalls: {
+      sameVersion: [
+        {
+          old: "Foo/preview/2025-04-01-preview/foo.json",
+          new: "Foo/preview/2025-04-01-preview/foo.json",
+        },
+        {
+          old: "Foo/stable/2025-01-01/foo.json",
+          new: "Foo/stable/2025-01-01/foo.json",
+        },
+        {
+          old: "Foo/stable/2025-03-01/foo.json",
+          new: "Foo/stable/2025-03-01/foo.json",
+        },
+      ],
+      crossVersion: [],
+    },
+  },
+  {
+    name: "modify multiple files, multiple versions",
+    changedFiles: {
+      modifications: [
+        "Bar/preview/2025-04-01-preview/bar.json",
+        "Bar/preview/2025-04-01-preview/baz.json",
+        "Bar/stable/2025-03-01/bar.json",
+        "Bar/stable/2025-03-01/baz.json",
+      ],
+    },
+    expectedCreateDummySwaggers: {
+      old: [],
+      new: [],
+    },
+    expectedOadCalls: {
+      sameVersion: [
+        {
+          old: "Bar/preview/2025-04-01-preview/bar.json",
+          new: "Bar/preview/2025-04-01-preview/bar.json",
+        },
+        {
+          old: "Bar/preview/2025-04-01-preview/baz.json",
+          new: "Bar/preview/2025-04-01-preview/baz.json",
+        },
+        {
+          old: "Bar/stable/2025-03-01/bar.json",
+          new: "Bar/stable/2025-03-01/bar.json",
+        },
+        {
+          old: "Bar/stable/2025-03-01/baz.json",
+          new: "Bar/stable/2025-03-01/baz.json",
+        },
+      ],
+      crossVersion: [],
+    },
+  },
+  {
+    name: "add new stable, one file",
+    changedFiles: {
+      additions: ["Foo/stable/2026-01-01/foo.json"],
+    },
+    expectedCreateDummySwaggers: {
+      old: [],
+      new: [],
+    },
+    expectedOadCalls: {
+      sameVersion: [],
+      crossVersion: [
+        {
+          old: "Foo/preview/2025-04-01-preview/foo.json",
+          new: "Foo/stable/2026-01-01/foo.json",
+        },
+        {
+          old: "Foo/stable/2025-03-01/foo.json",
+          new: "Foo/stable/2026-01-01/foo.json",
+        },
+      ],
+    },
+  },
+  {
+    name: "add new stable, multiple files",
+    changedFiles: {
+      additions: ["Bar/stable/2026-01-01/bar.json", "Bar/stable/2026-01-01/baz.json"],
+    },
+    expectedCreateDummySwaggers: {
+      old: [],
+      new: [],
+    },
+    expectedOadCalls: {
+      sameVersion: [],
+      crossVersion: [
+        {
+          old: "Bar/preview/2025-04-01-preview/bar.json",
+          new: "Bar/stable/2026-01-01/bar.json",
+        },
+        {
+          old: "Bar/preview/2025-04-01-preview/baz.json",
+          new: "Bar/stable/2026-01-01/baz.json",
+        },
+        {
+          old: "Bar/stable/2025-03-01/bar.json",
+          new: "Bar/stable/2026-01-01/bar.json",
+        },
+        {
+          old: "Bar/stable/2025-03-01/baz.json",
+          new: "Bar/stable/2026-01-01/baz.json",
+        },
+      ],
+    },
+  },
+  {
+    name: "rename one file, one version",
+    changedFiles: {
+      renames: [
+        {
+          from: "Foo/stable/2025-01-01/foo.json",
+          to: "Foo/stable/2025-01-01/openapi.json",
+        },
+      ],
+    },
+    // TODO: After code is fixed, should not create *any* dummy swaggers
+    expectedCreateDummySwaggers: {
+      old: ["Foo/stable/2025-01-01/openapi.json"],
+      new: ["Foo/stable/2025-01-01/foo.json"],
+    },
+    // TODO: After code is fixed, should only compare before and after renamed file
+    expectedOadCalls: {
+      sameVersion: [
+        {
+          old: "Foo/stable/2025-01-01/foo.json",
+          new: "Foo/stable/2025-01-01/foo.json",
+        },
+        {
+          old: "Foo/stable/2025-01-01/openapi.json",
+          new: "Foo/stable/2025-01-01/openapi.json",
+        },
+      ],
+      crossVersion: [],
+    },
+  },
+  // {
+  //   name: "rename one file, change case of service",
+  //   changedFiles: {
+  //     additions: ["foo/stable/2025-01-01/openapi.json"],
+  //     deletions: ["Foo/stable/2025-01-01/foo.json"],
+  //   },
+  //   // TODO: After code is fixed, should not create *any* dummy swaggers
+  //   expectedCreateDummySwaggers: {
+  //     old: [],
+  //     new: ["Foo/stable/2025-01-01/foo.json"],
+  //   },
+  //   // TODO: After code is fixed, should only compare before and after renamed file
+  //   expectedOadCalls: {
+  //     sameVersion: [
+  //       {
+  //         old: "Foo/stable/2025-01-01/foo.json",
+  //         new: "Foo/stable/2025-01-01/foo.json",
+  //       },
+  //     ],
+  //     crossVersion: [],
+  //   },
+  // },
+];
+
+describe("validateBreakingChange", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it.each(cases)(
+    "$name",
+    async ({ changedFiles, expectedCreateDummySwaggers, expectedOadCalls }) => {
+      // Prepend all input strings with the service parent folder (omitted from string literals for brevity)
+      // Use string concat instead of path.join(), since test inputs are all posix paths, and resolved at runtime
+      prependParentFolder(changedFiles, expectedCreateDummySwaggers, expectedOadCalls);
+
+      mockChangedFilesStatuses(changedFiles);
+
+      const mockCreateDummySwagger = vi.mocked(createDummySwagger);
+
+      const mockRunOad = vi.mocked(runOad).mockResolvedValue([]);
+
+      for (const data of [
+        {
+          runType: BREAKING_CHANGES_CHECK_TYPES.SAME_VERSION,
+          expectedOadCalls: expectedOadCalls.sameVersion,
+        },
+        {
+          runType: BREAKING_CHANGES_CHECK_TYPES.CROSS_VERSION,
+          expectedOadCalls: expectedOadCalls.crossVersion,
+        },
+      ]) {
+        mockRunOad.mockClear();
+
+        const statusCode = await validateBreakingChange({
+          ...context,
+          runType: data.runType,
+        });
+
+        expect(statusCode).toEqual(0);
+
+        for (const expected of expectedCreateDummySwaggers.old) {
+          expect(mockCreateDummySwagger).toBeCalledWith(
+            expect.anything(),
+            resolve(context.prInfo.tempRepoFolder, expected),
+          );
+        }
+
+        for (const expected of expectedCreateDummySwaggers.new) {
+          expect(mockCreateDummySwagger).toBeCalledWith(expect.anything(), resolve(expected));
+        }
+
+        expect(mockCreateDummySwagger).toBeCalledTimes(
+          expectedCreateDummySwaggers.old.length + expectedCreateDummySwaggers.new.length,
+        );
+
+        for (const expected of data.expectedOadCalls) {
+          expect(mockRunOad).toBeCalledWith(
+            path.join(context.prInfo.tempRepoFolder, expected.old),
+            expected.new,
+          );
+        }
+
+        expect(mockRunOad).toBeCalledTimes(data.expectedOadCalls.length);
+      }
+    },
+  );
+});
+
+function prependParentFolder(
+  changedFiles: {
+    additions?: string[];
+    modifications?: string[];
+    deletions?: string[];
+    renames?: {
+      from: string;
+      to: string;
+    }[];
+  },
+  expectedCreateDummySwaggers: { old: string[]; new: string[] },
+  expectedOadCalls: {
+    sameVersion: { old: string; new: string }[];
+    crossVersion: { old: string; new: string }[];
+  },
+) {
+  if (changedFiles.additions !== undefined) {
+    changedFiles.additions = changedFiles.additions?.map((p) => serviceParent + p);
+  }
+  if (changedFiles.modifications !== undefined) {
+    changedFiles.modifications = changedFiles.modifications?.map((p) => serviceParent + p);
+  }
+  if (changedFiles.deletions !== undefined) {
+    changedFiles.deletions = changedFiles.deletions?.map((p) => serviceParent + p);
+  }
+  if (changedFiles.renames !== undefined) {
+    changedFiles.renames = changedFiles.renames?.map((r) => ({
+      from: serviceParent + r.from,
+      to: serviceParent + r.to,
+    }));
+  }
+
+  expectedCreateDummySwaggers.old = expectedCreateDummySwaggers.old.map((p) => serviceParent + p);
+  expectedCreateDummySwaggers.new = expectedCreateDummySwaggers.new.map((p) => serviceParent + p);
+
+  expectedOadCalls.sameVersion = expectedOadCalls.sameVersion.map((c) => ({
+    old: serviceParent + c.old,
+    new: serviceParent + c.new,
+  }));
+  expectedOadCalls.crossVersion = expectedOadCalls.crossVersion.map((c) => ({
+    old: serviceParent + c.old,
+    new: serviceParent + c.new,
+  }));
+}
diff --git a/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/preview/2025-02-01-preview/bar.json b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/preview/2025-02-01-preview/bar.json
new file mode 100644
index 000000000000..0967ef424bce
--- /dev/null
+++ b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/preview/2025-02-01-preview/bar.json
@@ -0,0 +1 @@
+{}
diff --git a/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/preview/2025-02-01-preview/baz.json b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/preview/2025-02-01-preview/baz.json
new file mode 100644
index 000000000000..0967ef424bce
--- /dev/null
+++ b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/preview/2025-02-01-preview/baz.json
@@ -0,0 +1 @@
+{}
diff --git a/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/preview/2025-04-01-preview/bar.json b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/preview/2025-04-01-preview/bar.json
new file mode 100644
index 000000000000..0967ef424bce
--- /dev/null
+++ b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/preview/2025-04-01-preview/bar.json
@@ -0,0 +1 @@
+{}
diff --git a/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/preview/2025-04-01-preview/baz.json b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/preview/2025-04-01-preview/baz.json
new file mode 100644
index 000000000000..0967ef424bce
--- /dev/null
+++ b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/preview/2025-04-01-preview/baz.json
@@ -0,0 +1 @@
+{}
diff --git a/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/readme.md b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/readme.md
new file mode 100644
index 000000000000..68a0c931a3c1
--- /dev/null
+++ b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/readme.md
@@ -0,0 +1,54 @@
+# Bar
+
+> see https://aka.ms/autorest
+
+This is the AutoRest configuration file for Bar.
+
+## Configuration
+
+### Basic Information
+
+```yaml
+openapi-type: data-plane
+tag: package-2025-03-01
+```
+
+### Tag: package-2025-03-01
+
+These settings apply only when `--tag=package-2025-03-01` is specified on the command line.
+
+```yaml $(tag) == 'package-2025-03-01'
+input-file:
+  - stable/2025-03-01/bar.json
+  - stable/2025-03-01/baz.json
+```
+
+### Tag: package-2025-01-01
+
+These settings apply only when `--tag=package-2025-01-01` is specified on the command line.
+
+```yaml $(tag) == 'package-2025-01-01'
+input-file:
+  - stable/2025-01-01/bar.json
+  - stable/2025-01-01/baz.json
+```
+
+### Tag: package-2025-04-01-preview
+
+These settings apply only when `--tag=package-2025-04-01-preview` is specified on the command line.
+
+```yaml $(tag) == 'package-2025-04-01-preview'
+input-file:
+  - preview/2025-04-01-preview/bar.json
+  - preview/2025-04-01-preview/baz.json
+```
+
+### Tag: package-2025-02-01-preview
+
+These settings apply only when `--tag=package-2025-02-01-preview` is specified on the command line.
+
+```yaml $(tag) == 'package-2025-02-01-preview'
+input-file:
+  - preview/2025-02-01-preview/bar.json
+  - preview/2025-02-01-preview/baz.json
+```
\ No newline at end of file
diff --git a/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/stable/2025-01-01/bar.json b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/stable/2025-01-01/bar.json
new file mode 100644
index 000000000000..0967ef424bce
--- /dev/null
+++ b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/stable/2025-01-01/bar.json
@@ -0,0 +1 @@
+{}
diff --git a/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/stable/2025-01-01/baz.json b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/stable/2025-01-01/baz.json
new file mode 100644
index 000000000000..0967ef424bce
--- /dev/null
+++ b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/stable/2025-01-01/baz.json
@@ -0,0 +1 @@
+{}
diff --git a/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/stable/2025-03-01/bar.json b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/stable/2025-03-01/bar.json
new file mode 100644
index 000000000000..0967ef424bce
--- /dev/null
+++ b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/stable/2025-03-01/bar.json
@@ -0,0 +1 @@
+{}
diff --git a/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/stable/2025-03-01/baz.json b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/stable/2025-03-01/baz.json
new file mode 100644
index 000000000000..0967ef424bce
--- /dev/null
+++ b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Bar/stable/2025-03-01/baz.json
@@ -0,0 +1 @@
+{}
diff --git a/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Foo/preview/2025-02-01-preview/foo.json b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Foo/preview/2025-02-01-preview/foo.json
new file mode 100644
index 000000000000..0967ef424bce
--- /dev/null
+++ b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Foo/preview/2025-02-01-preview/foo.json
@@ -0,0 +1 @@
+{}
diff --git a/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Foo/preview/2025-04-01-preview/foo.json b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Foo/preview/2025-04-01-preview/foo.json
new file mode 100644
index 000000000000..0967ef424bce
--- /dev/null
+++ b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Foo/preview/2025-04-01-preview/foo.json
@@ -0,0 +1 @@
+{}
diff --git a/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Foo/readme.md b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Foo/readme.md
new file mode 100644
index 000000000000..3ed7b0f26309
--- /dev/null
+++ b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Foo/readme.md
@@ -0,0 +1,50 @@
+# Foo
+
+> see https://aka.ms/autorest
+
+This is the AutoRest configuration file for Foo.
+
+## Configuration
+
+### Basic Information
+
+```yaml
+openapi-type: data-plane
+tag: package-2025-03-01
+```
+
+### Tag: package-2025-03-01
+
+These settings apply only when `--tag=package-2025-03-01` is specified on the command line.
+
+```yaml $(tag) == 'package-2025-03-01'
+input-file:
+  - stable/2025-03-01/foo.json
+```
+
+### Tag: package-2025-01-01
+
+These settings apply only when `--tag=package-2025-01-01` is specified on the command line.
+
+```yaml $(tag) == 'package-2025-01-01'
+input-file:
+  - stable/2025-01-01/foo.json
+```
+
+### Tag: package-2025-04-01-preview
+
+These settings apply only when `--tag=package-2025-04-01-preview` is specified on the command line.
+
+```yaml $(tag) == 'package-2025-04-01-preview'
+input-file:
+  - preview/2025-04-01-preview/foo.json
+```
+
+### Tag: package-2025-02-01-preview
+
+These settings apply only when `--tag=package-2025-02-01-preview` is specified on the command line.
+
+```yaml $(tag) == 'package-2025-02-01-preview'
+input-file:
+  - preview/2025-02-01-preview/foo.json
+```
\ No newline at end of file
diff --git a/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Foo/stable/2025-01-01/foo.json b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Foo/stable/2025-01-01/foo.json
new file mode 100644
index 000000000000..0967ef424bce
--- /dev/null
+++ b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Foo/stable/2025-01-01/foo.json
@@ -0,0 +1 @@
+{}
diff --git a/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Foo/stable/2025-03-01/foo.json b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Foo/stable/2025-03-01/foo.json
new file mode 100644
index 000000000000..0967ef424bce
--- /dev/null
+++ b/eng/tools/openapi-diff-runner/test/fixtures/specification/foo/data-plane/Foo/stable/2025-03-01/foo.json
@@ -0,0 +1 @@
+{}