Clear env vars, sys props before test (#2659)

Avoids picking up values that were set by other tests using the same env
variables and system properties.

Also use AssertJ matchers in tests.

Author: dagnir

core/auth/src/test/java/software/amazon/awssdk/auth/credentials/internal/Ec2MetadataConfigProviderEndpointOverrideTest.java

@@ -15,8 +15,8 @@
 
 package software.amazon.awssdk.auth.credentials.internal;
 
-import static org.hamcrest.CoreMatchers.equalTo;
-import static org.junit.Assert.assertThat;
+import static org.assertj.core.api.Assertions.assertThat;
+
 import java.util.Arrays;
 import org.junit.After;
 import org.junit.Before;
@@ -67,6 +67,9 @@ public static Iterable<Object> testCases() {
 
     @Before
     public void setup() {
+        ENVIRONMENT_VARIABLE_HELPER.reset();
+        System.clearProperty(SdkSystemSetting.AWS_EC2_METADATA_SERVICE_ENDPOINT.property());
+
         if (testCase.envEndpointOverride != null) {
             ENVIRONMENT_VARIABLE_HELPER.set(SdkSystemSetting.AWS_EC2_METADATA_SERVICE_ENDPOINT.environmentVariable(),
                     testCase.envEndpointOverride);
@@ -97,7 +100,7 @@ public void teardown() {
     public void resolvesCorrectEndpointOverride() {
         String endpointOverride = Ec2MetadataConfigProvider.builder().build().getEndpointOverride();
 
-        assertThat(endpointOverride, equalTo(testCase.expectedEndpointOverride));
+        assertThat(endpointOverride).isEqualTo(testCase.expectedEndpointOverride);
     }
 
     private static String getTestFilePath(String testFile) {

core/auth/src/test/java/software/amazon/awssdk/auth/credentials/internal/Ec2MetadataConfigProviderEndpointResolutionTest.java

@@ -15,8 +15,8 @@
 
 package software.amazon.awssdk.auth.credentials.internal;
 
-import static org.hamcrest.CoreMatchers.equalTo;
-import static org.junit.Assert.assertThat;
+import static org.assertj.core.api.Assertions.assertThat;
+
 import java.util.Arrays;
 import org.junit.Before;
 import org.junit.Test;
@@ -63,7 +63,7 @@ public void setup() {
 
     @Test
     public void resolvesCorrectEndpoint() {
-        assertThat(Ec2MetadataConfigProvider.builder().build().getEndpoint(), equalTo(testCase.expectedEndpoint));
+        assertThat(Ec2MetadataConfigProvider.builder().build().getEndpoint()).isEqualTo(testCase.expectedEndpoint);
     }
 
     private static class TestCase {