diff --git a/phpcs.xml.dist b/phpcs.xml.dist
index b9824c5..5b1d2ee 100644
--- a/phpcs.xml.dist
+++ b/phpcs.xml.dist
@@ -6,6 +6,7 @@
 
     <exclude-pattern>tests/data/*</exclude-pattern>
     <exclude-pattern>tests/functions.php</exclude-pattern>
+    <exclude-pattern>tests/WP_UnitTestCase_Base.php</exclude-pattern>
 
     <rule ref="PSR12NeutronRuleset">
         <exclude name="Generic.Files.LineLength"/>
@@ -15,6 +16,7 @@
 
     <!-- PHPCS does not understand yield -->
     <rule ref="NeutronStandard.Functions.TypeHint.UnusedReturnType">
+        <exclude-pattern>tests/AssertMethodTypeSpecifyingExtensionTest.php</exclude-pattern>
         <exclude-pattern>tests/DynamicReturnTypeExtensionTest.php</exclude-pattern>
     </rule>
 </ruleset>
diff --git a/src/AssertNotWpErrorTypeSpecifyingExtension.php b/src/AssertNotWpErrorTypeSpecifyingExtension.php
index e512e72..401f684 100644
--- a/src/AssertNotWpErrorTypeSpecifyingExtension.php
+++ b/src/AssertNotWpErrorTypeSpecifyingExtension.php
@@ -29,23 +29,19 @@ public function getClass(): string
 
     public function isMethodSupported(MethodReflection $methodReflection, MethodCall $node, TypeSpecifierContext $context): bool
     {
-        return strtolower($methodReflection->getName()) === 'assertNotWPError'
+        return strtolower($methodReflection->getName()) === 'assertnotwperror'
             && isset($node->args[0])
-            && !$context->null();
+            && $context->null();
     }
 
     // phpcs:ignore SlevomatCodingStandard.Functions.UnusedParameter
     public function specifyTypes(MethodReflection $methodReflection, MethodCall $node, Scope $scope, TypeSpecifierContext $context): SpecifiedTypes
     {
-        if ($context->null()) {
-            throw new \PHPStan\ShouldNotHappenException();
-        }
-
         $expr = $node->getArgs()[0]->value;
         $typeBefore = $scope->getType($expr);
         $type = TypeCombinator::remove($typeBefore, new ObjectType('WP_Error'));
 
-        return $this->typeSpecifier->create($expr, $type, $context);
+        return $this->typeSpecifier->create($expr, $type, TypeSpecifierContext::createTruthy());
     }
 
     public function setTypeSpecifier(TypeSpecifier $typeSpecifier): void
diff --git a/src/AssertWpErrorTypeSpecifyingExtension.php b/src/AssertWpErrorTypeSpecifyingExtension.php
index e0608cb..27db6ce 100644
--- a/src/AssertWpErrorTypeSpecifyingExtension.php
+++ b/src/AssertWpErrorTypeSpecifyingExtension.php
@@ -28,21 +28,17 @@ public function getClass(): string
 
     public function isMethodSupported(MethodReflection $methodReflection, MethodCall $node, TypeSpecifierContext $context): bool
     {
-        return strtolower($methodReflection->getName()) === 'assertWPError'
+        return strtolower($methodReflection->getName()) === 'assertwperror'
             && isset($node->args[0])
-            && !$context->null();
+            && $context->null();
     }
 
     // phpcs:ignore SlevomatCodingStandard.Functions.UnusedParameter
     public function specifyTypes(MethodReflection $methodReflection, MethodCall $node, Scope $scope, TypeSpecifierContext $context): SpecifiedTypes
     {
-        if ($context->null()) {
-            throw new \PHPStan\ShouldNotHappenException();
-        }
-
         $args = $node->getArgs();
 
-        return $this->typeSpecifier->create($args[0]->value, new ObjectType('WP_Error'), $context);
+        return $this->typeSpecifier->create($args[0]->value, new ObjectType('WP_Error'), TypeSpecifierContext::createTruthy());
     }
 
     public function setTypeSpecifier(TypeSpecifier $typeSpecifier): void
diff --git a/tests/WP_UnitTestCase_Base.php b/tests/WP_UnitTestCase_Base.php
new file mode 100644
index 0000000..6079da0
--- /dev/null
+++ b/tests/WP_UnitTestCase_Base.php
@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+use PHPUnit\Framework\TestCase;
+
+class WP_UnitTestCase_Base extends TestCase
+{
+    /**
+     * Asserts that the given value is an instance of WP_Error.
+     *
+     * @param mixed  $actual  The value to check.
+     * @param string $message Optional. Message to display when the assertion fails.
+     * @return void
+     */
+    public function assertWPError( $actual, $message = '' ) {
+    }
+
+    /**
+     * Asserts that the given value is not an instance of WP_Error.
+     *
+     * @param mixed  $actual  The value to check.
+     * @param string $message Optional. Message to display when the assertion fails.
+     * @return void
+     */
+    public function assertNotWPError( $actual, $message = '' ) {
+    }
+}
diff --git a/tests/data/assert_not_wp_error.php b/tests/data/assert_not_wp_error.php
index f603607..07ca30f 100644
--- a/tests/data/assert_not_wp_error.php
+++ b/tests/data/assert_not_wp_error.php
@@ -4,15 +4,16 @@
 
 namespace SzepeViktor\PHPStan\WordPress\Tests;
 
+use WP_UnitTestCase_Base;
 use function PHPStan\Testing\assertType;
 
-class Foo
+class AssertNotWpError
 {
 
     public function inheritedAssertMethodsNarrowType(): void
     {
         /** @var \WP_Error|int $no */
-        $no = $no;
+        $no = $_GET['no'];
 
         $customAsserter = new class () extends WP_UnitTestCase_Base {};
         $customAsserter->assertNotWPError($no);
diff --git a/tests/data/assert_wp_error.php b/tests/data/assert_wp_error.php
index 93b6462..7785805 100644
--- a/tests/data/assert_wp_error.php
+++ b/tests/data/assert_wp_error.php
@@ -4,15 +4,16 @@
 
 namespace SzepeViktor\PHPStan\WordPress\Tests;
 
+use WP_UnitTestCase_Base;
 use function PHPStan\Testing\assertType;
 
-class Foo
+class AssertWpError
 {
 
     public function inheritedAssertMethodsNarrowType(): void
     {
         /** @var \WP_Error|int $yes */
-        $yes = $yes;
+        $yes = $_GET['yes'];
 
         $customAsserter = new class () extends WP_UnitTestCase_Base {};
         $customAsserter->assertWPError($yes);