diff --git a/src/cargo/sources/registry/index.rs b/src/cargo/sources/registry/index.rs
index 46078c5a3b0..9d47091b29a 100644
--- a/src/cargo/sources/registry/index.rs
+++ b/src/cargo/sources/registry/index.rs
@@ -300,6 +300,12 @@ impl<'cfg> RegistryIndex<'cfg> {
         let summaries = summaries
             .iter()
             .filter(|&(summary, yanked)| {
+                // Note: This particular logic can cause problems with
+                // optional dependencies when offline. If at least 1 version
+                // of an optional dependency is downloaded, but that version
+                // does not satisfy the requirements, then resolution will
+                // fail. Unfortunately, whether or not something is optional
+                // is not known here.
                 (online || load.is_crate_downloaded(summary.package_id()))
                     && (!yanked || {
                         log::debug!("{:?}", yanked_whitelist);
diff --git a/src/cargo/sources/registry/remote.rs b/src/cargo/sources/registry/remote.rs
index 9a1933c13bd..7a0dcbf9b59 100644
--- a/src/cargo/sources/registry/remote.rs
+++ b/src/cargo/sources/registry/remote.rs
@@ -176,6 +176,18 @@ impl<'cfg> RegistryData for RemoteRegistry<'cfg> {
 
     fn update_index(&mut self) -> CargoResult<()> {
         if self.config.cli_unstable().offline {
+            if self.repo()?.is_empty()? {
+                // An empty repository is guaranteed to fail, since hitting
+                // this path means we need at least one crate. This is an
+                // attempt to provide a better error message other than "no
+                // matching package named …".
+                failure::bail!(
+                    "unable to fetch {} in offline mode\n\
+                     Try running without the offline flag, or try running \
+                     `cargo fetch` within your project directory before going offline.",
+                    self.source_id
+                );
+            }
             return Ok(());
         }
         if self.config.cli_unstable().no_index_update {
diff --git a/tests/testsuite/build.rs b/tests/testsuite/build.rs
index cb7d021254a..f6aabe544e2 100644
--- a/tests/testsuite/build.rs
+++ b/tests/testsuite/build.rs
@@ -956,261 +956,6 @@ Did you mean `a`?",
         .run();
 }
 
-#[test]
-fn cargo_compile_path_with_offline() {
-    let p = project()
-        .file(
-            "Cargo.toml",
-            r#"
-            [package]
-            name = "foo"
-            version = "0.0.1"
-            authors = []
-
-            [dependencies.bar]
-            path = "bar"
-        "#,
-        )
-        .file("src/lib.rs", "")
-        .file("bar/Cargo.toml", &basic_manifest("bar", "0.0.1"))
-        .file("bar/src/lib.rs", "")
-        .build();
-
-    p.cargo("build -Zoffline")
-        .masquerade_as_nightly_cargo()
-        .run();
-}
-
-#[test]
-fn cargo_compile_with_downloaded_dependency_with_offline() {
-    Package::new("present_dep", "1.2.3")
-        .file("Cargo.toml", &basic_manifest("present_dep", "1.2.3"))
-        .file("src/lib.rs", "")
-        .publish();
-
-    {
-        // make package downloaded
-        let p = project()
-            .file(
-                "Cargo.toml",
-                r#"
-            [project]
-            name = "foo"
-            version = "0.1.0"
-
-            [dependencies]
-            present_dep = "1.2.3"
-        "#,
-            )
-            .file("src/lib.rs", "")
-            .build();
-        p.cargo("build").run();
-    }
-
-    let p2 = project()
-        .at("bar")
-        .file(
-            "Cargo.toml",
-            r#"
-            [project]
-            name = "bar"
-            version = "0.1.0"
-
-            [dependencies]
-            present_dep = "1.2.3"
-        "#,
-        )
-        .file("src/lib.rs", "")
-        .build();
-
-    p2.cargo("build -Zoffline")
-        .masquerade_as_nightly_cargo()
-        .with_stderr(
-            "\
-[COMPILING] present_dep v1.2.3
-[COMPILING] bar v0.1.0 ([..])
-[FINISHED] dev [unoptimized + debuginfo] target(s) in [..]",
-        )
-        .run();
-}
-
-#[test]
-fn cargo_compile_offline_not_try_update() {
-    let p = project()
-        .at("bar")
-        .file(
-            "Cargo.toml",
-            r#"
-            [project]
-            name = "bar"
-            version = "0.1.0"
-
-            [dependencies]
-            not_cached_dep = "1.2.5"
-        "#,
-        )
-        .file("src/lib.rs", "")
-        .build();
-
-    p.cargo("build -Zoffline")
-        .masquerade_as_nightly_cargo()
-        .with_status(101)
-        .with_stderr(
-            "\
-error: no matching package named `not_cached_dep` found
-location searched: registry `[..]`
-required by package `bar v0.1.0 ([..])`
-As a reminder, you're using offline mode (-Z offline) \
-which can sometimes cause surprising resolution failures, \
-if this error is too confusing you may wish to retry \
-without the offline flag.",
-        )
-        .run();
-}
-
-#[test]
-fn compile_offline_without_maxvers_cached() {
-    Package::new("present_dep", "1.2.1").publish();
-    Package::new("present_dep", "1.2.2").publish();
-
-    Package::new("present_dep", "1.2.3")
-        .file("Cargo.toml", &basic_manifest("present_dep", "1.2.3"))
-        .file(
-            "src/lib.rs",
-            r#"pub fn get_version()->&'static str {"1.2.3"}"#,
-        )
-        .publish();
-
-    Package::new("present_dep", "1.2.5")
-        .file("Cargo.toml", &basic_manifest("present_dep", "1.2.5"))
-        .file("src/lib.rs", r#"pub fn get_version(){"1.2.5"}"#)
-        .publish();
-
-    {
-        // make package cached
-        let p = project()
-            .file(
-                "Cargo.toml",
-                r#"
-            [project]
-            name = "foo"
-            version = "0.1.0"
-
-            [dependencies]
-            present_dep = "=1.2.3"
-        "#,
-            )
-            .file("src/lib.rs", "")
-            .build();
-        p.cargo("build").run();
-    }
-
-    let p2 = project()
-        .file(
-            "Cargo.toml",
-            r#"
-            [project]
-            name = "foo"
-            version = "0.1.0"
-
-            [dependencies]
-            present_dep = "1.2"
-        "#,
-        )
-        .file(
-            "src/main.rs",
-            "\
-extern crate present_dep;
-fn main(){
-    println!(\"{}\", present_dep::get_version());
-}",
-        )
-        .build();
-
-    p2.cargo("run -Zoffline")
-        .masquerade_as_nightly_cargo()
-        .with_stderr(
-            "\
-[COMPILING] present_dep v1.2.3
-[COMPILING] foo v0.1.0 ([CWD])
-[FINISHED] dev [unoptimized + debuginfo] target(s) in [..]
-     Running `[..]`",
-        )
-        .with_stdout("1.2.3")
-        .run();
-}
-
-#[test]
-fn offline_unused_target_dep() {
-    // -Z offline with a target dependency that is not used and not downloaded.
-    Package::new("unused_dep", "1.0.0").publish();
-    Package::new("used_dep", "1.0.0").publish();
-    let p = project()
-        .file(
-            "Cargo.toml",
-            r#"
-            [project]
-            name = "foo"
-            version = "0.1.0"
-            [dependencies]
-            used_dep = "1.0"
-            [target.'cfg(unused)'.dependencies]
-            unused_dep = "1.0"
-            "#,
-        )
-        .file("src/lib.rs", "")
-        .build();
-    // Do a build that downloads only what is necessary.
-    p.cargo("build")
-        .with_stderr_contains("[DOWNLOADED] used_dep [..]")
-        .with_stderr_does_not_contain("[DOWNLOADED] unused_dep [..]")
-        .run();
-    p.cargo("clean").run();
-    // Build offline, make sure it works.
-    p.cargo("build -Z offline")
-        .masquerade_as_nightly_cargo()
-        .run();
-}
-
-#[test]
-fn offline_missing_optional() {
-    Package::new("opt_dep", "1.0.0").publish();
-    let p = project()
-        .file(
-            "Cargo.toml",
-            r#"
-            [project]
-            name = "foo"
-            version = "0.1.0"
-            [dependencies]
-            opt_dep = { version = "1.0", optional = true }
-            "#,
-        )
-        .file("src/lib.rs", "")
-        .build();
-    // Do a build that downloads only what is necessary.
-    p.cargo("build")
-        .with_stderr_does_not_contain("[DOWNLOADED] opt_dep [..]")
-        .run();
-    p.cargo("clean").run();
-    // Build offline, make sure it works.
-    p.cargo("build -Z offline")
-        .masquerade_as_nightly_cargo()
-        .run();
-    p.cargo("build -Z offline --features=opt_dep")
-        .masquerade_as_nightly_cargo()
-        .with_stderr(
-            "\
-[ERROR] failed to download `opt_dep v1.0.0`
-
-Caused by:
-  can't make HTTP request in the offline mode
-",
-        )
-        .with_status(101)
-        .run();
-}
-
 #[test]
 fn incompatible_dependencies() {
     Package::new("bad", "0.1.0").publish();
@@ -1310,58 +1055,6 @@ failed to select a version for `bad` which could resolve this conflict",
         .run();
 }
 
-#[test]
-fn compile_offline_while_transitive_dep_not_cached() {
-    let baz = Package::new("baz", "1.0.0");
-    let baz_path = baz.archive_dst();
-    baz.publish();
-
-    let mut content = Vec::new();
-
-    let mut file = File::open(baz_path.clone()).ok().unwrap();
-    let _ok = file.read_to_end(&mut content).ok().unwrap();
-    drop(file);
-    drop(File::create(baz_path.clone()).ok().unwrap());
-
-    Package::new("bar", "0.1.0").dep("baz", "1.0.0").publish();
-
-    let p = project()
-        .file(
-            "Cargo.toml",
-            r#"
-            [project]
-            name = "foo"
-            version = "0.0.1"
-
-            [dependencies]
-            bar = "0.1.0"
-        "#,
-        )
-        .file("src/main.rs", "fn main(){}")
-        .build();
-
-    // simulate download bar, but fail to download baz
-    p.cargo("build")
-        .with_status(101)
-        .with_stderr_contains("[..]failed to verify the checksum of `baz[..]")
-        .run();
-
-    drop(File::create(baz_path).ok().unwrap().write_all(&content));
-
-    p.cargo("build -Zoffline")
-        .masquerade_as_nightly_cargo()
-        .with_status(101)
-        .with_stderr(
-            "\
-[ERROR] failed to download `baz v1.0.0`
-
-Caused by:
-  can't make HTTP request in the offline mode
-",
-        )
-        .run();
-}
-
 #[test]
 fn compile_path_dep_then_change_version() {
     let p = project()
diff --git a/tests/testsuite/git.rs b/tests/testsuite/git.rs
index 934af0b722e..62ed8cfbd0d 100644
--- a/tests/testsuite/git.rs
+++ b/tests/testsuite/git.rs
@@ -83,175 +83,6 @@ fn cargo_compile_simple_git_dep() {
         .run();
 }
 
-#[test]
-fn cargo_compile_forbird_git_httpsrepo_offline() {
-    let p = project()
-        .file(
-            "Cargo.toml",
-            r#"
-
-            [project]
-            name = "foo"
-            version = "0.5.0"
-            authors = ["chabapok@example.com"]
-
-            [dependencies.dep1]
-            git = 'https://github.com/some_user/dep1.git'
-        "#,
-        )
-        .file("src/main.rs", "")
-        .build();
-
-    p.cargo("build -Zoffline").masquerade_as_nightly_cargo().with_status(101).
-                    with_stderr("\
-error: failed to load source for a dependency on `dep1`
-
-Caused by:
-  Unable to update https://github.com/some_user/dep1.git
-
-Caused by:
-  can't checkout from 'https://github.com/some_user/dep1.git': you are in the offline mode (-Z offline)").run();
-}
-
-#[test]
-fn cargo_compile_offline_with_cached_git_dep() {
-    let git_project = git::new("dep1", |project| {
-        project
-            .file("Cargo.toml", &basic_lib_manifest("dep1"))
-            .file(
-                "src/lib.rs",
-                r#"
-                pub static COOL_STR:&str = "cached git repo rev1";
-            "#,
-            )
-    })
-    .unwrap();
-
-    let repo = git2::Repository::open(&git_project.root()).unwrap();
-    let rev1 = repo.revparse_single("HEAD").unwrap().id();
-
-    // Commit the changes and make sure we trigger a recompile
-    File::create(&git_project.root().join("src/lib.rs"))
-        .unwrap()
-        .write_all(br#"pub static COOL_STR:&str = "cached git repo rev2";"#)
-        .unwrap();
-    git::add(&repo);
-    let rev2 = git::commit(&repo);
-
-    {
-        // cache to registry rev1 and rev2
-        let prj = project()
-            .at("cache_git_dep")
-            .file(
-                "Cargo.toml",
-                &format!(
-                    r#"
-            [project]
-            name = "cache_git_dep"
-            version = "0.5.0"
-
-            [dependencies.dep1]
-            git = '{}'
-            rev = "{}"
-            "#,
-                    git_project.url(),
-                    rev1
-                ),
-            )
-            .file("src/main.rs", "fn main(){}")
-            .build();
-        prj.cargo("build").run();
-
-        File::create(&prj.root().join("Cargo.toml"))
-            .unwrap()
-            .write_all(
-                format!(
-                    r#"
-            [project]
-            name = "cache_git_dep"
-            version = "0.5.0"
-
-            [dependencies.dep1]
-            git = '{}'
-            rev = "{}"
-            "#,
-                    git_project.url(),
-                    rev2
-                )
-                .as_bytes(),
-            )
-            .unwrap();
-        prj.cargo("build").run();
-    }
-
-    let p = project()
-        .file(
-            "Cargo.toml",
-            &format!(
-                r#"
-            [project]
-            name = "foo"
-            version = "0.5.0"
-
-            [dependencies.dep1]
-            git = '{}'
-        "#,
-                git_project.url()
-            ),
-        )
-        .file(
-            "src/main.rs",
-            &main_file(r#""hello from {}", dep1::COOL_STR"#, &["dep1"]),
-        )
-        .build();
-
-    let git_root = git_project.root();
-
-    p.cargo("build -Zoffline")
-        .masquerade_as_nightly_cargo()
-        .with_stderr(format!(
-            "\
-[COMPILING] dep1 v0.5.0 ({}#[..])
-[COMPILING] foo v0.5.0 ([CWD])
-[FINISHED] dev [unoptimized + debuginfo] target(s) in [..]",
-            path2url(git_root),
-        ))
-        .run();
-
-    assert!(p.bin("foo").is_file());
-
-    p.process(&p.bin("foo"))
-        .with_stdout("hello from cached git repo rev2\n")
-        .run();
-
-    File::create(&p.root().join("Cargo.toml"))
-        .unwrap()
-        .write_all(
-            format!(
-                r#"
-        [project]
-        name = "foo"
-        version = "0.5.0"
-
-        [dependencies.dep1]
-        git = '{}'
-        rev = "{}"
-    "#,
-                git_project.url(),
-                rev1
-            )
-            .as_bytes(),
-        )
-        .unwrap();
-
-    p.cargo("build -Zoffline")
-        .masquerade_as_nightly_cargo()
-        .run();
-    p.process(&p.bin("foo"))
-        .with_stdout("hello from cached git repo rev1\n")
-        .run();
-}
-
 #[test]
 fn cargo_compile_git_dep_branch() {
     let project = project();
diff --git a/tests/testsuite/main.rs b/tests/testsuite/main.rs
index 74c767a150c..5dcf126ec82 100644
--- a/tests/testsuite/main.rs
+++ b/tests/testsuite/main.rs
@@ -56,6 +56,7 @@ mod metabuild;
 mod metadata;
 mod net_config;
 mod new;
+mod offline;
 mod out_dir;
 mod overrides;
 mod package;
diff --git a/tests/testsuite/offline.rs b/tests/testsuite/offline.rs
new file mode 100644
index 00000000000..91653135d66
--- /dev/null
+++ b/tests/testsuite/offline.rs
@@ -0,0 +1,548 @@
+use crate::support::{basic_manifest, git, main_file, path2url, project, registry::Package};
+use std::fs;
+
+#[test]
+fn offline_unused_target_dep() {
+    // -Z offline with a target dependency that is not used and not downloaded.
+    Package::new("unused_dep", "1.0.0").publish();
+    Package::new("used_dep", "1.0.0").publish();
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [project]
+            name = "foo"
+            version = "0.1.0"
+            [dependencies]
+            used_dep = "1.0"
+            [target.'cfg(unused)'.dependencies]
+            unused_dep = "1.0"
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+    // Do a build that downloads only what is necessary.
+    p.cargo("build")
+        .with_stderr_contains("[DOWNLOADED] used_dep [..]")
+        .with_stderr_does_not_contain("[DOWNLOADED] unused_dep [..]")
+        .run();
+    p.cargo("clean").run();
+    // Build offline, make sure it works.
+    p.cargo("build -Z offline")
+        .masquerade_as_nightly_cargo()
+        .run();
+}
+
+#[test]
+fn offline_missing_optional() {
+    Package::new("opt_dep", "1.0.0").publish();
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [project]
+            name = "foo"
+            version = "0.1.0"
+            [dependencies]
+            opt_dep = { version = "1.0", optional = true }
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+    // Do a build that downloads only what is necessary.
+    p.cargo("build")
+        .with_stderr_does_not_contain("[DOWNLOADED] opt_dep [..]")
+        .run();
+    p.cargo("clean").run();
+    // Build offline, make sure it works.
+    p.cargo("build -Z offline")
+        .masquerade_as_nightly_cargo()
+        .run();
+    p.cargo("build -Z offline --features=opt_dep")
+        .masquerade_as_nightly_cargo()
+        .with_stderr(
+            "\
+[ERROR] failed to download `opt_dep v1.0.0`
+
+Caused by:
+  can't make HTTP request in the offline mode
+",
+        )
+        .with_status(101)
+        .run();
+}
+
+#[test]
+fn cargo_compile_path_with_offline() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [package]
+            name = "foo"
+            version = "0.0.1"
+            authors = []
+
+            [dependencies.bar]
+            path = "bar"
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .file("bar/Cargo.toml", &basic_manifest("bar", "0.0.1"))
+        .file("bar/src/lib.rs", "")
+        .build();
+
+    p.cargo("build -Zoffline")
+        .masquerade_as_nightly_cargo()
+        .run();
+}
+
+#[test]
+fn cargo_compile_with_downloaded_dependency_with_offline() {
+    Package::new("present_dep", "1.2.3")
+        .file("Cargo.toml", &basic_manifest("present_dep", "1.2.3"))
+        .file("src/lib.rs", "")
+        .publish();
+
+    // make package downloaded
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [project]
+            name = "foo"
+            version = "0.1.0"
+
+            [dependencies]
+            present_dep = "1.2.3"
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+    p.cargo("build").run();
+
+    let p2 = project()
+        .at("bar")
+        .file(
+            "Cargo.toml",
+            r#"
+            [project]
+            name = "bar"
+            version = "0.1.0"
+
+            [dependencies]
+            present_dep = "1.2.3"
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+
+    p2.cargo("build -Zoffline")
+        .masquerade_as_nightly_cargo()
+        .with_stderr(
+            "\
+[COMPILING] present_dep v1.2.3
+[COMPILING] bar v0.1.0 ([..])
+[FINISHED] dev [unoptimized + debuginfo] target(s) in [..]",
+        )
+        .run();
+}
+
+#[test]
+fn cargo_compile_offline_not_try_update() {
+    let p = project()
+        .at("bar")
+        .file(
+            "Cargo.toml",
+            r#"
+            [project]
+            name = "bar"
+            version = "0.1.0"
+
+            [dependencies]
+            not_cached_dep = "1.2.5"
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+
+    p.cargo("build -Zoffline")
+        .masquerade_as_nightly_cargo()
+        .with_status(101)
+        .with_stderr(
+            "\
+[ERROR] failed to load source for a dependency on `not_cached_dep`
+
+Caused by:
+  Unable to update registry `https://github.com/rust-lang/crates.io-index`
+
+Caused by:
+  unable to fetch registry `https://github.com/rust-lang/crates.io-index` in offline mode
+Try running without the offline flag, or try running `cargo fetch` within your \
+project directory before going offline.
+",
+        )
+        .run();
+}
+
+#[test]
+fn compile_offline_without_maxvers_cached() {
+    Package::new("present_dep", "1.2.1").publish();
+    Package::new("present_dep", "1.2.2").publish();
+
+    Package::new("present_dep", "1.2.3")
+        .file("Cargo.toml", &basic_manifest("present_dep", "1.2.3"))
+        .file(
+            "src/lib.rs",
+            r#"pub fn get_version()->&'static str {"1.2.3"}"#,
+        )
+        .publish();
+
+    Package::new("present_dep", "1.2.5")
+        .file("Cargo.toml", &basic_manifest("present_dep", "1.2.5"))
+        .file("src/lib.rs", r#"pub fn get_version(){"1.2.5"}"#)
+        .publish();
+
+    // make package cached
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [project]
+            name = "foo"
+            version = "0.1.0"
+
+            [dependencies]
+            present_dep = "=1.2.3"
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+    p.cargo("build").run();
+
+    let p2 = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [project]
+            name = "foo"
+            version = "0.1.0"
+
+            [dependencies]
+            present_dep = "1.2"
+            "#,
+        )
+        .file(
+            "src/main.rs",
+            "\
+extern crate present_dep;
+fn main(){
+    println!(\"{}\", present_dep::get_version());
+}",
+        )
+        .build();
+
+    p2.cargo("run -Zoffline")
+        .masquerade_as_nightly_cargo()
+        .with_stderr(
+            "\
+[COMPILING] present_dep v1.2.3
+[COMPILING] foo v0.1.0 ([CWD])
+[FINISHED] dev [unoptimized + debuginfo] target(s) in [..]
+     Running `[..]`",
+        )
+        .with_stdout("1.2.3")
+        .run();
+}
+
+#[test]
+fn cargo_compile_forbird_git_httpsrepo_offline() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+
+            [project]
+            name = "foo"
+            version = "0.5.0"
+            authors = ["chabapok@example.com"]
+
+            [dependencies.dep1]
+            git = 'https://github.com/some_user/dep1.git'
+            "#,
+        )
+        .file("src/main.rs", "")
+        .build();
+
+    p.cargo("build -Zoffline").masquerade_as_nightly_cargo().with_status(101).
+                    with_stderr("\
+error: failed to load source for a dependency on `dep1`
+
+Caused by:
+  Unable to update https://github.com/some_user/dep1.git
+
+Caused by:
+  can't checkout from 'https://github.com/some_user/dep1.git': you are in the offline mode (-Z offline)").run();
+}
+
+#[test]
+fn compile_offline_while_transitive_dep_not_cached() {
+    let baz = Package::new("baz", "1.0.0");
+    let baz_path = baz.archive_dst();
+    baz.publish();
+
+    let baz_content = fs::read(&baz_path).unwrap();
+    // Truncate the file to simulate a download failure.
+    fs::write(&baz_path, &[]).unwrap();
+
+    Package::new("bar", "0.1.0").dep("baz", "1.0.0").publish();
+
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [project]
+            name = "foo"
+            version = "0.0.1"
+
+            [dependencies]
+            bar = "0.1.0"
+            "#,
+        )
+        .file("src/main.rs", "fn main(){}")
+        .build();
+
+    // simulate download bar, but fail to download baz
+    p.cargo("build")
+        .with_status(101)
+        .with_stderr_contains("[..]failed to verify the checksum of `baz[..]")
+        .run();
+
+    // Restore the file contents.
+    fs::write(&baz_path, &baz_content).unwrap();
+
+    p.cargo("build -Zoffline")
+        .masquerade_as_nightly_cargo()
+        .with_status(101)
+        .with_stderr(
+            "\
+[ERROR] failed to download `baz v1.0.0`
+
+Caused by:
+  can't make HTTP request in the offline mode
+",
+        )
+        .run();
+}
+
+#[test]
+fn update_offline() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [project]
+            name = "foo"
+            version = "0.0.1"
+            authors = []
+
+            [dependencies]
+            bar = "*"
+            "#,
+        )
+        .file("src/main.rs", "fn main() {}")
+        .build();
+    p.cargo("update -Zoffline")
+        .masquerade_as_nightly_cargo()
+        .with_status(101)
+        .with_stderr("error: you can't update in the offline mode[..]")
+        .run();
+}
+
+#[test]
+fn cargo_compile_offline_with_cached_git_dep() {
+    let git_project = git::new("dep1", |project| {
+        project
+            .file("Cargo.toml", &basic_manifest("dep1", "0.5.0"))
+            .file(
+                "src/lib.rs",
+                r#"
+                pub static COOL_STR:&str = "cached git repo rev1";
+                "#,
+            )
+    })
+    .unwrap();
+
+    let repo = git2::Repository::open(&git_project.root()).unwrap();
+    let rev1 = repo.revparse_single("HEAD").unwrap().id();
+
+    // Commit the changes and make sure we trigger a recompile
+    git_project.change_file(
+        "src/lib.rs",
+        r#"pub static COOL_STR:&str = "cached git repo rev2";"#,
+    );
+    git::add(&repo);
+    let rev2 = git::commit(&repo);
+
+    // cache to registry rev1 and rev2
+    let prj = project()
+        .at("cache_git_dep")
+        .file(
+            "Cargo.toml",
+            &format!(
+                r#"
+                [project]
+                name = "cache_git_dep"
+                version = "0.5.0"
+
+                [dependencies.dep1]
+                git = '{}'
+                rev = "{}"
+                "#,
+                git_project.url(),
+                rev1
+            ),
+        )
+        .file("src/main.rs", "fn main(){}")
+        .build();
+    prj.cargo("build").run();
+
+    prj.change_file(
+        "Cargo.toml",
+        &format!(
+            r#"
+            [project]
+            name = "cache_git_dep"
+            version = "0.5.0"
+
+            [dependencies.dep1]
+            git = '{}'
+            rev = "{}"
+            "#,
+            git_project.url(),
+            rev2
+        ),
+    );
+    prj.cargo("build").run();
+
+    let p = project()
+        .file(
+            "Cargo.toml",
+            &format!(
+                r#"
+                [project]
+                name = "foo"
+                version = "0.5.0"
+
+                [dependencies.dep1]
+                git = '{}'
+                "#,
+                git_project.url()
+            ),
+        )
+        .file(
+            "src/main.rs",
+            &main_file(r#""hello from {}", dep1::COOL_STR"#, &["dep1"]),
+        )
+        .build();
+
+    let git_root = git_project.root();
+
+    p.cargo("build -Zoffline")
+        .masquerade_as_nightly_cargo()
+        .with_stderr(format!(
+            "\
+[COMPILING] dep1 v0.5.0 ({}#[..])
+[COMPILING] foo v0.5.0 ([CWD])
+[FINISHED] dev [unoptimized + debuginfo] target(s) in [..]",
+            path2url(git_root),
+        ))
+        .run();
+
+    assert!(p.bin("foo").is_file());
+
+    p.process(&p.bin("foo"))
+        .with_stdout("hello from cached git repo rev2\n")
+        .run();
+
+    p.change_file(
+        "Cargo.toml",
+        &format!(
+            r#"
+            [project]
+            name = "foo"
+            version = "0.5.0"
+
+            [dependencies.dep1]
+            git = '{}'
+            rev = "{}"
+            "#,
+            git_project.url(),
+            rev1
+        ),
+    );
+
+    p.cargo("build -Zoffline")
+        .masquerade_as_nightly_cargo()
+        .run();
+    p.process(&p.bin("foo"))
+        .with_stdout("hello from cached git repo rev1\n")
+        .run();
+}
+
+#[test]
+fn offline_resolve_optional_fail() {
+    // Example where resolve fails offline.
+    //
+    // This happens if at least 1 version of an optional dependency is
+    // available, but none of them satisfy the requirements. The current logic
+    // that handles this is `RegistryIndex::query_inner`, and it doesn't know
+    // if the package being queried is an optional one. This is not ideal, it
+    // would be best if it just ignored optional (unselected) dependencies.
+    Package::new("dep", "1.0.0").publish();
+
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [package]
+            name = "foo"
+            version = "0.1.0"
+
+            [dependencies]
+            dep = { version = "1.0", optional = true }
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .build();
+
+    p.cargo("fetch").run();
+
+    // Change dep to 2.0.
+    p.change_file(
+        "Cargo.toml",
+            r#"
+            [package]
+            name = "foo"
+            version = "0.1.0"
+
+            [dependencies]
+            dep = { version = "2.0", optional = true }
+            "#,
+    );
+
+    p.cargo("build -Z offline")
+        .masquerade_as_nightly_cargo()
+        .with_status(101)
+        .with_stderr("\
+[ERROR] failed to select a version for the requirement `dep = \"^2.0\"`
+  candidate versions found which didn't match: 1.0.0
+  location searched: `[..]` index (which is replacing registry `https://github.com/rust-lang/crates.io-index`)
+required by package `foo v0.1.0 ([..]/foo)`
+perhaps a crate was updated and forgotten to be re-vendored?
+As a reminder, you're using offline mode (-Z offline) which can sometimes cause \
+surprising resolution failures, if this error is too confusing you may wish to \
+retry without the offline flag.
+")
+        .run();
+}
diff --git a/tests/testsuite/registry.rs b/tests/testsuite/registry.rs
index 4330e1ddec0..c99f081092d 100644
--- a/tests/testsuite/registry.rs
+++ b/tests/testsuite/registry.rs
@@ -819,30 +819,6 @@ fn update_lockfile() {
         .run();
 }
 
-#[test]
-fn update_offline() {
-    let p = project()
-        .file(
-            "Cargo.toml",
-            r#"
-            [project]
-            name = "foo"
-            version = "0.0.1"
-            authors = []
-
-            [dependencies]
-            bar = "*"
-        "#,
-        )
-        .file("src/main.rs", "fn main() {}")
-        .build();
-    p.cargo("update -Zoffline")
-        .masquerade_as_nightly_cargo()
-        .with_status(101)
-        .with_stderr("error: you can't update in the offline mode[..]")
-        .run();
-}
-
 #[test]
 fn dev_dependency_not_used() {
     let p = project()