diff --git a/src/diff-informed-analysis-utils.test.ts b/src/diff-informed-analysis-utils.test.ts
new file mode 100644
index 000000000..1125f18fd
--- /dev/null
+++ b/src/diff-informed-analysis-utils.test.ts
@@ -0,0 +1,185 @@
+import test, { ExecutionContext } from "ava";
+import * as sinon from "sinon";
+
+import * as actionsUtil from "./actions-util";
+import type { PullRequestBranches } from "./actions-util";
+import * as apiClient from "./api-client";
+import { shouldPerformDiffInformedAnalysis } from "./diff-informed-analysis-utils";
+import { Feature, Features } from "./feature-flags";
+import { getRunnerLogger } from "./logging";
+import { parseRepositoryNwo } from "./repository";
+import {
+  setupTests,
+  mockCodeQLVersion,
+  mockFeatureFlagApiEndpoint,
+  setupActionsVars,
+} from "./testing-utils";
+import { GitHubVariant, withTmpDir } from "./util";
+import type { GitHubVersion } from "./util";
+
+setupTests(test);
+
+interface DiffInformedAnalysisTestCase {
+  featureEnabled: boolean;
+  gitHubVersion: GitHubVersion;
+  pullRequestBranches: PullRequestBranches;
+  codeQLVersion: string;
+  diffInformedQueriesEnvVar?: boolean;
+}
+
+const defaultTestCase: DiffInformedAnalysisTestCase = {
+  featureEnabled: true,
+  gitHubVersion: {
+    type: GitHubVariant.DOTCOM,
+  },
+  pullRequestBranches: {
+    base: "main",
+    head: "feature-branch",
+  },
+  codeQLVersion: "2.21.0",
+};
+
+const testShouldPerformDiffInformedAnalysis = test.macro({
+  exec: async (
+    t: ExecutionContext,
+    _title: string,
+    partialTestCase: Partial<DiffInformedAnalysisTestCase>,
+    expectedResult: boolean,
+  ) => {
+    return await withTmpDir(async (tmpDir) => {
+      setupActionsVars(tmpDir, tmpDir);
+
+      const testCase = { ...defaultTestCase, ...partialTestCase };
+      const logger = getRunnerLogger(true);
+      const codeql = mockCodeQLVersion(testCase.codeQLVersion);
+
+      if (testCase.diffInformedQueriesEnvVar !== undefined) {
+        process.env.CODEQL_ACTION_DIFF_INFORMED_QUERIES =
+          testCase.diffInformedQueriesEnvVar.toString();
+      } else {
+        delete process.env.CODEQL_ACTION_DIFF_INFORMED_QUERIES;
+      }
+
+      const features = new Features(
+        testCase.gitHubVersion,
+        parseRepositoryNwo("github/example"),
+        tmpDir,
+        logger,
+      );
+      mockFeatureFlagApiEndpoint(200, {
+        [Feature.DiffInformedQueries]: testCase.featureEnabled,
+      });
+
+      const getGitHubVersionStub = sinon
+        .stub(apiClient, "getGitHubVersion")
+        .resolves(testCase.gitHubVersion);
+      const getPullRequestBranchesStub = sinon
+        .stub(actionsUtil, "getPullRequestBranches")
+        .returns(testCase.pullRequestBranches);
+
+      const result = await shouldPerformDiffInformedAnalysis(
+        codeql,
+        features,
+        logger,
+      );
+
+      t.is(result, expectedResult);
+
+      delete process.env.CODEQL_ACTION_DIFF_INFORMED_QUERIES;
+
+      getGitHubVersionStub.restore();
+      getPullRequestBranchesStub.restore();
+    });
+  },
+  title: (_, title) => `shouldPerformDiffInformedAnalysis: ${title}`,
+});
+
+test(
+  testShouldPerformDiffInformedAnalysis,
+  "returns true in the default test case",
+  {},
+  true,
+);
+
+test(
+  testShouldPerformDiffInformedAnalysis,
+  "returns false when feature flag is disabled from the API",
+  {
+    featureEnabled: false,
+  },
+  false,
+);
+
+test(
+  testShouldPerformDiffInformedAnalysis,
+  "returns false when CODEQL_ACTION_DIFF_INFORMED_QUERIES is set to false",
+  {
+    featureEnabled: true,
+    diffInformedQueriesEnvVar: false,
+  },
+  false,
+);
+
+test(
+  testShouldPerformDiffInformedAnalysis,
+  "returns true when CODEQL_ACTION_DIFF_INFORMED_QUERIES is set to true",
+  {
+    featureEnabled: false,
+    diffInformedQueriesEnvVar: true,
+  },
+  true,
+);
+
+test(
+  testShouldPerformDiffInformedAnalysis,
+  "returns false for CodeQL version 2.20.0",
+  {
+    codeQLVersion: "2.20.0",
+  },
+  false,
+);
+
+test(
+  testShouldPerformDiffInformedAnalysis,
+  "returns false for invalid GHES version",
+  {
+    gitHubVersion: {
+      type: GitHubVariant.GHES,
+      version: "invalid-version",
+    },
+  },
+  false,
+);
+
+test(
+  testShouldPerformDiffInformedAnalysis,
+  "returns false for GHES version 3.18.5",
+  {
+    gitHubVersion: {
+      type: GitHubVariant.GHES,
+      version: "3.18.5",
+    },
+  },
+  false,
+);
+
+test(
+  testShouldPerformDiffInformedAnalysis,
+  "returns true for GHES version 3.19.0",
+  {
+    gitHubVersion: {
+      type: GitHubVariant.GHES,
+      version: "3.19.0",
+    },
+  },
+  true,
+);
+
+test(
+  testShouldPerformDiffInformedAnalysis,
+  "returns false when not a pull request",
+  {
+    pullRequestBranches: undefined,
+  },
+  false,
+);