diff --git a/tests/unit/db-core-extended.test.ts b/tests/unit/db-core-extended.test.ts
index af765807ac..b38b567d06 100644
--- a/tests/unit/db-core-extended.test.ts
+++ b/tests/unit/db-core-extended.test.ts
@@ -66,10 +66,11 @@ test("getDbInstance returns same instance on second call (singleton)", async ()
 
 test("resetDbInstance allows getting a fresh instance", async () => {
   await resetStorage();
-  const db1 = core.getDbInstance();
+  core.getDbInstance();
   core.resetDbInstance();
   const db2 = core.getDbInstance();
-  assert.ok(db1 !== db2 || true);
+  assert.ok(db2);
+  assert.ok(typeof db2.prepare === "function");
 });
 
 test("closeDbInstance closes the database", async () => {
diff --git a/tests/unit/db-models-extended.test.ts b/tests/unit/db-models-extended.test.ts
index db6adb8f78..201d9d88a3 100644
--- a/tests/unit/db-models-extended.test.ts
+++ b/tests/unit/db-models-extended.test.ts
@@ -124,10 +124,10 @@ test("getModelPreserveOpenAIDeveloperRole returns boolean or undefined", async (
   assert.ok(result === undefined || typeof result === "boolean");
 });
 
-test("getModelUpstreamExtraHeaders returns null or object", async () => {
+test("getModelUpstreamExtraHeaders returns empty object when no overrides", async () => {
   await resetStorage();
   const result = models.getModelUpstreamExtraHeaders("openai", "gpt-4o");
-  assert.ok(result === null || typeof result === "object");
+  assert.deepEqual(result, {});
 });
 
 test("removeModelCompatOverride does not throw for unknown provider/model", async () => {
diff --git a/tests/unit/db-settings-extended.test.ts b/tests/unit/db-settings-extended.test.ts
index c8d6582e6f..6bb476a573 100644
--- a/tests/unit/db-settings-extended.test.ts
+++ b/tests/unit/db-settings-extended.test.ts
@@ -69,7 +69,7 @@ test("getPricing returns an object", async () => {
 test("getPricingForModel returns null for unknown model", async () => {
   await resetStorage();
   const result = await settings.getPricingForModel("unknown-provider", "unknown-model");
-  assert.ok(result === null || result === undefined || typeof result === "object");
+  assert.equal(result, null);
 });
 
 test("updatePricing stores pricing data", async () => {
@@ -120,7 +120,7 @@ test("setProxyConfig stores proxy configuration", async () => {
 test("getProxyForLevel returns null for unset level", async () => {
   await resetStorage();
   const result = await settings.getProxyForLevel("global");
-  assert.ok(result === null || result === undefined || typeof result === "object");
+  assert.equal(result, null);
 });
 
 test("setProxyForLevel stores proxy for level", async () => {
@@ -138,11 +138,8 @@ test("deleteProxyForLevel removes proxy", async () => {
   assert.ok(result === null || result === undefined);
 });
 
-test("bumpProxyConfigGeneration increments generation", () => {
-  const gen1 = (settings as any).proxyConfigGeneration;
-  settings.bumpProxyConfigGeneration();
-  const gen2 = (settings as any).proxyConfigGeneration;
-  assert.ok(gen2 === undefined || gen2 > gen1 || true);
+test("bumpProxyConfigGeneration does not throw", () => {
+  assert.doesNotThrow(() => settings.bumpProxyConfigGeneration());
 });
 
 test("isCloudEnabled returns boolean", async () => {
diff --git a/tests/unit/executor-base-utils.test.ts b/tests/unit/executor-base-utils.test.ts
index 7ff1d8d92c..d3727c205e 100644
--- a/tests/unit/executor-base-utils.test.ts
+++ b/tests/unit/executor-base-utils.test.ts
@@ -116,17 +116,32 @@ test("mergeAbortSignals aborts when secondary fires", () => {
   assert.ok(merged.aborted);
 });
 
-test("sanitizeReasoningEffortForProvider clamps values", () => {
-  const result = base.sanitizeReasoningEffortForProvider("high", "openai");
-  assert.ok(result === "high" || result === "medium" || result === "low" || typeof result === "string");
+test("sanitizeReasoningEffortForProvider passes through body without reasoning_effort", () => {
+  const body = { model: "gpt-4o", temperature: 0.7 };
+  const result = base.sanitizeReasoningEffortForProvider(body, "openai", "gpt-4o");
+  assert.deepEqual(result, body);
 });
 
-test("sanitizeReasoningEffortForProvider handles null", () => {
-  const result = base.sanitizeReasoningEffortForProvider(null, "openai");
-  assert.ok(result === null || result === undefined || typeof result === "string");
+test("sanitizeReasoningEffortForProvider clamps xhigh to high for unsupported providers", () => {
+  const body = { reasoning_effort: "xhigh" };
+  const result = base.sanitizeReasoningEffortForProvider(body, "openai", "gpt-4o") as any;
+  assert.equal(result.reasoning_effort, "high");
 });
 
-test("sanitizeReasoningEffortForProvider handles undefined", () => {
-  const result = base.sanitizeReasoningEffortForProvider(undefined, "anthropic");
-  assert.ok(result === null || result === undefined || typeof result === "string");
+test("sanitizeReasoningEffortForProvider preserves high effort", () => {
+  const body = { reasoning_effort: "high" };
+  const result = base.sanitizeReasoningEffortForProvider(body, "openai", "gpt-4o") as any;
+  assert.equal(result.reasoning_effort, "high");
+});
+
+test("sanitizeReasoningEffortForProvider preserves medium effort", () => {
+  const body = { reasoning_effort: "medium" };
+  const result = base.sanitizeReasoningEffortForProvider(body, "openai", "gpt-4o") as any;
+  assert.equal(result.reasoning_effort, "medium");
+});
+
+test("sanitizeReasoningEffortForProvider returns non-object body as-is", () => {
+  assert.equal(base.sanitizeReasoningEffortForProvider(null, "openai", "gpt-4o"), null);
+  assert.equal(base.sanitizeReasoningEffortForProvider("string", "openai", "gpt-4o"), "string");
+  assert.equal(base.sanitizeReasoningEffortForProvider(42, "openai", "gpt-4o"), 42);
 });
diff --git a/tests/unit/model-resolver.test.ts b/tests/unit/model-resolver.test.ts
index 007a97d3a6..2e4b860d8b 100644
--- a/tests/unit/model-resolver.test.ts
+++ b/tests/unit/model-resolver.test.ts
@@ -18,9 +18,9 @@ test("resolveProviderAlias returns known alias", () => {
   assert.ok(result === "claude" || result === "anthropic" || typeof result === "string");
 });
 
-test("resolveProviderAlias returns null for unknown alias", () => {
+test("resolveProviderAlias returns input string for unknown alias", () => {
   const result = model.resolveProviderAlias("totally-unknown-provider");
-  assert.ok(result === null || typeof result === "string");
+  assert.equal(result, "totally-unknown-provider");
 });
 
 test("parseModel parses provider/model format", () => {
@@ -68,12 +68,13 @@ test("normalizeCrossProxyModelId handles undefined", () => {
 });
 
 test("resolveCanonicalProviderModel returns object for known model", () => {
-  const result = model.resolveCanonicalProviderModel("gpt-4o");
+  const result = model.resolveCanonicalProviderModel("openai", "gpt-4o");
   assert.ok(typeof result === "object");
+  assert.ok(result !== null);
 });
 
-test("resolveCanonicalProviderModel returns object for null", () => {
-  const result = model.resolveCanonicalProviderModel(null);
+test("resolveCanonicalProviderModel handles null modelId", () => {
+  const result = model.resolveCanonicalProviderModel("openai", null);
   assert.ok(typeof result === "object");
 });
 
diff --git a/tests/unit/stream-payload-collector.test.ts b/tests/unit/stream-payload-collector.test.ts
index 5543c2a436..1cb9e58b85 100644
--- a/tests/unit/stream-payload-collector.test.ts
+++ b/tests/unit/stream-payload-collector.test.ts
@@ -42,18 +42,19 @@ test("buildStreamSummaryFromEvents handles empty array", () => {
 });
 
 test("buildStreamSummaryFromEvents handles single event", () => {
-  const events = [{ data: '{"choices":[{"delta":{"content":"hello"}}]}' }];
-  const result = collector.buildStreamSummaryFromEvents(events);
+  const events = [{ data: { choices: [{ delta: { content: "hello" } }] } }];
+  const result = collector.buildStreamSummaryFromEvents(events) as any;
+  assert.ok(result !== null);
   assert.ok(typeof result === "object");
 });
 
 test("buildStreamSummaryFromEvents handles multiple events", () => {
   const events = [
-    { data: '{"choices":[{"delta":{"content":"hello"}}]}' },
-    { data: '{"choices":[{"delta":{"content":" world"}}]}' },
-    { data: "[DONE]" },
+    { data: { choices: [{ delta: { content: "hello" } }] } },
+    { data: { choices: [{ delta: { content: " world" } }] } },
   ];
-  const result = collector.buildStreamSummaryFromEvents(events);
+  const result = collector.buildStreamSummaryFromEvents(events) as any;
+  assert.ok(result !== null);
   assert.ok(typeof result === "object");
 });