Rewrite TestBuildCopySingleFileToExistDir to not use fixtures

Signed-off-by: Alexandr Morozov <lk4d4@docker.com>

integration-cli/build_tests/TestCopy/SingleFileToExistDir/Dockerfile

@@ -1,10 +0,0 @@
-FROM busybox
-RUN echo 'dockerio:x:1001:1001::/bin:/bin/false' >> /etc/passwd
-RUN echo 'dockerio:x:1001:' >> /etc/group
-RUN mkdir /exists
-RUN touch /exists/exists_file
-RUN chown -R dockerio.dockerio /exists
-COPY test_file /exists/
-RUN [ $(ls -l / | grep exists | awk '{print $3":"$4}') = 'dockerio:dockerio' ]
-RUN [ $(ls -l /exists/test_file | awk '{print $3":"$4}') = 'root:root' ]
-RUN [ $(ls -l /exists/exists_file | awk '{print $3":"$4}') = 'dockerio:dockerio' ]

integration-cli/docker_cli_build_test.go

@@ -687,13 +687,27 @@ COPY test_file .`,
 }
 
 func TestBuildCopySingleFileToExistDir(t *testing.T) {
-	buildDirectory := filepath.Join(workingDirectory, "build_tests", "TestCopy")
-	if out, _, err := dockerCmdInDir(t, buildDirectory, "build", "-t", "testcopyimg", "SingleFileToExistDir"); err != nil {
-		t.Fatalf("build failed to complete: %s, %v", out, err)
+	name := "testcopysinglefiletoexistdir"
+	defer deleteImages(name)
+	ctx, err := fakeContext(`FROM busybox
+RUN echo 'dockerio:x:1001:1001::/bin:/bin/false' >> /etc/passwd
+RUN echo 'dockerio:x:1001:' >> /etc/group
+RUN mkdir /exists
+RUN touch /exists/exists_file
+RUN chown -R dockerio.dockerio /exists
+COPY test_file /exists/
+RUN [ $(ls -l / | grep exists | awk '{print $3":"$4}') = 'dockerio:dockerio' ]
+RUN [ $(ls -l /exists/test_file | awk '{print $3":"$4}') = 'root:root' ]
+RUN [ $(ls -l /exists/exists_file | awk '{print $3":"$4}') = 'dockerio:dockerio' ]`,
+		map[string]string{
+			"test_file": "test1",
+		})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := buildImageFromContext(name, ctx, true); err != nil {
+		t.Fatal(err)
 	}
-
-	deleteImages("testcopyimg")
-
 	logDone("build - copy single file to existing dir")
 }