diff --git a/tests/testsuite/build.rs b/tests/testsuite/build.rs
index 2d1e47424..e60bf21c4 100644
--- a/tests/testsuite/build.rs
+++ b/tests/testsuite/build.rs
@@ -6,7 +6,7 @@ use crate::support::paths::{root, CargoPathExt};
 use crate::support::registry::Package;
 use crate::support::ProjectBuilder;
 use crate::support::{
-    basic_bin_manifest, basic_lib_manifest, basic_manifest, is_nightly, rustc_host, sleep_ms,
+    basic_bin_manifest, basic_lib_manifest, basic_manifest, rustc_host, sleep_ms,
 };
 use crate::support::{main_file, project, Execs};
 use cargo::util::paths::dylib_path_envvar;
@@ -2706,10 +2706,6 @@ fn example_as_dylib() {
 
 #[test]
 fn example_as_proc_macro() {
-    if !is_nightly() {
-        return;
-    }
-
     let p = project()
         .file(
             "Cargo.toml",
@@ -2725,7 +2721,18 @@ fn example_as_proc_macro() {
         "#,
         )
         .file("src/lib.rs", "")
-        .file("examples/ex.rs", "#![feature(proc_macro)]")
+        .file(
+            "examples/ex.rs",
+            r#"
+            extern crate proc_macro;
+            use proc_macro::TokenStream;
+
+            #[proc_macro]
+            pub fn eat(_item: TokenStream) -> TokenStream {
+                "".parse().unwrap()
+            }
+            "#,
+        )
         .build();
 
     p.cargo("build --example=ex").run();
diff --git a/tests/testsuite/cross_compile.rs b/tests/testsuite/cross_compile.rs
index 686b28414..6e9623aba 100644
--- a/tests/testsuite/cross_compile.rs
+++ b/tests/testsuite/cross_compile.rs
@@ -149,6 +149,7 @@ fn plugin_deps() {
         return;
     }
     if !is_nightly() {
+        // plugins are unstable
         return;
     }
 
@@ -241,6 +242,7 @@ fn plugin_to_the_max() {
         return;
     }
     if !is_nightly() {
+        // plugins are unstable
         return;
     }
 
@@ -396,6 +398,7 @@ fn plugin_with_extra_dylib_dep() {
         return;
     }
     if !is_nightly() {
+        // plugins are unstable
         return;
     }
 
diff --git a/tests/testsuite/custom_target.rs b/tests/testsuite/custom_target.rs
index d05661aca..2b392f8ac 100644
--- a/tests/testsuite/custom_target.rs
+++ b/tests/testsuite/custom_target.rs
@@ -4,6 +4,7 @@ use crate::support::{basic_manifest, project};
 #[test]
 fn custom_target_minimal() {
     if !is_nightly() {
+        // Requires features no_core, lang_items
         return;
     }
     let p = project()
@@ -53,6 +54,7 @@ fn custom_target_minimal() {
 #[test]
 fn custom_target_dependency() {
     if !is_nightly() {
+        // Requires features no_core, lang_items, optin_builtin_traits
         return;
     }
     let p = project()
diff --git a/tests/testsuite/doc.rs b/tests/testsuite/doc.rs
index b073a070c..210db61f3 100644
--- a/tests/testsuite/doc.rs
+++ b/tests/testsuite/doc.rs
@@ -903,9 +903,6 @@ fn document_only_lib() {
 
 #[test]
 fn plugins_no_use_target() {
-    if !is_nightly() {
-        return;
-    }
     let p = project()
         .file(
             "Cargo.toml",
@@ -1165,11 +1162,6 @@ fn doc_workspace_open_binary_and_library() {
 
 #[test]
 fn doc_edition() {
-    if !is_nightly() {
-        // Stable rustdoc won't have the edition option. Remove this once it
-        // is stabilized.
-        return;
-    }
     let p = project()
         .file(
             "Cargo.toml",
@@ -1198,9 +1190,6 @@ fn doc_edition() {
 
 #[test]
 fn doc_target_edition() {
-    if !is_nightly() {
-        return;
-    }
     let p = project()
         .file(
             "Cargo.toml",
diff --git a/tests/testsuite/edition.rs b/tests/testsuite/edition.rs
index 3652318be..69f45c421 100644
--- a/tests/testsuite/edition.rs
+++ b/tests/testsuite/edition.rs
@@ -1,11 +1,7 @@
-use crate::support::{basic_lib_manifest, is_nightly, project};
+use crate::support::{basic_lib_manifest, project};
 
 #[test]
 fn edition_works_for_build_script() {
-    if !is_nightly() {
-        return;
-    }
-
     let p = project()
         .file(
             "Cargo.toml",
diff --git a/tests/testsuite/fix.rs b/tests/testsuite/fix.rs
index 574ef5a2b..a1c335f8c 100644
--- a/tests/testsuite/fix.rs
+++ b/tests/testsuite/fix.rs
@@ -3,7 +3,6 @@ use std::fs::File;
 use git2;
 
 use crate::support::git;
-use crate::support::is_nightly;
 use crate::support::{basic_manifest, project};
 
 use std::io::Write;
@@ -267,15 +266,11 @@ fn do_not_fix_non_relevant_deps() {
 
 #[test]
 fn prepare_for_2018() {
-    if !is_nightly() {
-        return;
-    }
     let p = project()
         .file(
             "src/lib.rs",
             r#"
                 #![allow(unused)]
-                #![feature(rust_2018_preview)]
 
                 mod foo {
                     pub const FOO: &str = "fooo";
@@ -311,15 +306,10 @@ fn prepare_for_2018() {
 
 #[test]
 fn local_paths() {
-    if !is_nightly() {
-        return;
-    }
     let p = project()
         .file(
             "src/lib.rs",
             r#"
-                #![feature(rust_2018_preview)]
-
                 use test::foo;
 
                 mod test {
@@ -350,9 +340,6 @@ fn local_paths() {
 
 #[test]
 fn upgrade_extern_crate() {
-    if !is_nightly() {
-        return;
-    }
     let p = project()
         .file(
             "Cargo.toml",
@@ -403,15 +390,11 @@ fn upgrade_extern_crate() {
 
 #[test]
 fn specify_rustflags() {
-    if !is_nightly() {
-        return;
-    }
     let p = project()
         .file(
             "src/lib.rs",
             r#"
                 #![allow(unused)]
-                #![feature(rust_2018_preview)]
 
                 mod foo {
                     pub const FOO: &str = "fooo";
@@ -874,15 +857,10 @@ information about transitioning to the 2018 edition see:
 
 #[test]
 fn fix_overlapping() {
-    if !is_nightly() {
-        return;
-    }
     let p = project()
         .file(
             "src/lib.rs",
             r#"
-                #![feature(rust_2018_preview)]
-
                 pub fn foo<T>() {}
                 pub struct A;
 
@@ -912,9 +890,6 @@ fn fix_overlapping() {
 
 #[test]
 fn fix_idioms() {
-    if !is_nightly() {
-        return;
-    }
     let p = project()
         .file(
             "Cargo.toml",
@@ -1196,9 +1171,6 @@ fn only_warn_for_relevant_crates() {
 
 #[test]
 fn fix_to_broken_code() {
-    if !is_nightly() {
-        return;
-    }
     let p = project()
         .file(
             "foo/Cargo.toml",
diff --git a/tests/testsuite/install.rs b/tests/testsuite/install.rs
index 6a893e46a..a991d8e2e 100644
--- a/tests/testsuite/install.rs
+++ b/tests/testsuite/install.rs
@@ -770,11 +770,6 @@ fn installs_from_cwd_by_default() {
 
 #[test]
 fn installs_from_cwd_with_2018_warnings() {
-    if !support::is_nightly() {
-        // Stable rust won't have the edition option. Remove this once it
-        // is stabilized.
-        return;
-    }
     let p = project()
         .file(
             "Cargo.toml",
diff --git a/tests/testsuite/package.rs b/tests/testsuite/package.rs
index 78bea4f55..fca74f071 100644
--- a/tests/testsuite/package.rs
+++ b/tests/testsuite/package.rs
@@ -6,7 +6,7 @@ use std::path::Path;
 use crate::support::cargo_process;
 use crate::support::registry::Package;
 use crate::support::{
-    basic_manifest, git, is_nightly, path2url, paths, project, publish::validate_crate_contents,
+    basic_manifest, git, path2url, paths, project, publish::validate_crate_contents,
     registry,
 };
 use git2;
@@ -972,11 +972,6 @@ fn test_edition() {
 
 #[test]
 fn edition_with_metadata() {
-    if !is_nightly() {
-        // --edition is nightly-only
-        return;
-    }
-
     let p = project()
         .file(
             "Cargo.toml",
diff --git a/tests/testsuite/plugins.rs b/tests/testsuite/plugins.rs
index bd58ebc6b..7cd31c9bd 100644
--- a/tests/testsuite/plugins.rs
+++ b/tests/testsuite/plugins.rs
@@ -4,6 +4,7 @@ use crate::support::{is_nightly, rustc_host};
 #[test]
 fn plugin_to_the_max() {
     if !is_nightly() {
+        // plugins are unstable
         return;
     }
 
@@ -103,6 +104,7 @@ fn plugin_to_the_max() {
 #[test]
 fn plugin_with_dynamic_native_dependency() {
     if !is_nightly() {
+        // plugins are unstable
         return;
     }
 
@@ -335,6 +337,7 @@ fn native_plugin_dependency_with_custom_ar_linker() {
 #[test]
 fn panic_abort_plugins() {
     if !is_nightly() {
+        // requires rustc_private
         return;
     }
 
@@ -382,6 +385,7 @@ fn panic_abort_plugins() {
 #[test]
 fn shared_panic_abort_plugins() {
     if !is_nightly() {
+        // requires rustc_private
         return;
     }
 
diff --git a/tests/testsuite/proc_macro.rs b/tests/testsuite/proc_macro.rs
index 370765f9d..43a8ad986 100644
--- a/tests/testsuite/proc_macro.rs
+++ b/tests/testsuite/proc_macro.rs
@@ -204,6 +204,7 @@ fn impl_and_derive() {
 #[test]
 fn plugin_and_proc_macro() {
     if !is_nightly() {
+        // plugins are unstable
         return;
     }
 
diff --git a/tests/testsuite/profiles.rs b/tests/testsuite/profiles.rs
index 21510f383..dd5608a05 100644
--- a/tests/testsuite/profiles.rs
+++ b/tests/testsuite/profiles.rs
@@ -1,6 +1,5 @@
 use std::env;
 
-use crate::support::is_nightly;
 use crate::support::project;
 
 #[test]
@@ -149,10 +148,6 @@ fn check_opt_level_override(profile_level: &str, rustc_level: &str) {
 
 #[test]
 fn opt_level_overrides() {
-    if !is_nightly() {
-        return;
-    }
-
     for &(profile_level, rustc_level) in &[
         ("1", "1"),
         ("2", "2"),
diff --git a/tests/testsuite/run.rs b/tests/testsuite/run.rs
index f5394c17a..a16613e98 100644
--- a/tests/testsuite/run.rs
+++ b/tests/testsuite/run.rs
@@ -1,4 +1,3 @@
-use crate::support;
 use crate::support::{basic_bin_manifest, basic_lib_manifest, project, Project};
 use cargo::util::paths::dylib_path_envvar;
 
@@ -435,10 +434,6 @@ fn autodiscover_examples_project(rust_edition: &str, autoexamples: Option<bool>)
 
 #[test]
 fn run_example_autodiscover_2015() {
-    if !support::is_nightly() {
-        return;
-    }
-
     let p = autodiscover_examples_project("2015", None);
     p.cargo("run --example a")
         .with_status(101)
@@ -467,10 +462,6 @@ error: no example target named `a`
 
 #[test]
 fn run_example_autodiscover_2015_with_autoexamples_enabled() {
-    if !support::is_nightly() {
-        return;
-    }
-
     let p = autodiscover_examples_project("2015", Some(true));
     p.cargo("run --example a")
         .with_stderr(
@@ -485,10 +476,6 @@ fn run_example_autodiscover_2015_with_autoexamples_enabled() {
 
 #[test]
 fn run_example_autodiscover_2015_with_autoexamples_disabled() {
-    if !support::is_nightly() {
-        return;
-    }
-
     let p = autodiscover_examples_project("2015", Some(false));
     p.cargo("run --example a")
         .with_status(101)
@@ -498,10 +485,6 @@ fn run_example_autodiscover_2015_with_autoexamples_disabled() {
 
 #[test]
 fn run_example_autodiscover_2018() {
-    if !support::is_nightly() {
-        return;
-    }
-
     let p = autodiscover_examples_project("2018", None);
     p.cargo("run --example a")
         .with_stderr(
diff --git a/tests/testsuite/support/mod.rs b/tests/testsuite/support/mod.rs
index 7ac57311d..3a0264f82 100644
--- a/tests/testsuite/support/mod.rs
+++ b/tests/testsuite/support/mod.rs
@@ -60,6 +60,7 @@ rust, like this:
 
 ```
 if !is_nightly() {
+    // Add a comment here explaining why this is necessary.
     return;
 }
 ```
@@ -753,7 +754,6 @@ impl Execs {
                 p.cwd(cwd.join(path.as_ref()));
             } else {
                 p.cwd(path);
-
             }
         }
         self
diff --git a/tests/testsuite/test.rs b/tests/testsuite/test.rs
index b0ea361c8..413502d91 100644
--- a/tests/testsuite/test.rs
+++ b/tests/testsuite/test.rs
@@ -6,7 +6,7 @@ use cargo;
 use crate::support::paths::CargoPathExt;
 use crate::support::registry::Package;
 use crate::support::{basic_bin_manifest, basic_lib_manifest, basic_manifest, cargo_exe, project};
-use crate::support::{is_nightly, rustc_host, sleep_ms};
+use crate::support::{rustc_host, sleep_ms};
 
 #[test]
 fn cargo_test_simple() {
@@ -106,9 +106,6 @@ fn cargo_test_release() {
 
 #[test]
 fn cargo_test_overflow_checks() {
-    if !is_nightly() {
-        return;
-    }
     let p = project()
         .file(
             "Cargo.toml",