Improve zero tests messaging

Changelog.md

@@ -12,6 +12,11 @@
 * [#1257](https://github.com/mbj/mutant/pull/1257)
   Fix crash on numblock mutations.
 
+* [#1258](https://github.com/mbj/mutant/pull/1258)
+  Add improved UI on detecting 0 tests.
+  This should be beneficial in onboarding scenarios or after manual
+  persistend rspec selections.
+
 # v0.10.33 2021-08-25
 
 * [#1249](https://github.com/mbj/mutant/pull/1249/files)

lib/mutant/cli/command/environment/run.rb

@@ -7,7 +7,7 @@ class Environment
         class Run < self
           NAME              = 'run'
           SHORT_DESCRIPTION = 'Run code analysis'
-          SLEEP             = 40
+          SLEEP             = 60
           SUBCOMMANDS       = EMPTY_ARRAY
 
           UNLICENSED = <<~MESSAGE.lines.freeze
@@ -16,6 +16,20 @@ class Run < self
             See https://github.com/mbj/mutant#licensing
           MESSAGE
 
+          NO_TESTS_MESSAGE = <<~'MESSAGE'
+            ===============
+            Mutant found no tests. Mutation testing cannot be started.
+
+            This can have various reasons:
+
+            * You did not setup an integration, see:
+              https://github.com/mbj/mutant/blob/main/docs/configuration.md#integration
+            * You set environment variables like RSPEC_OPTS that filter out all tests.
+            * You set configuration optiosn like `config.filter_run :focus` which do
+              make rspec to not report any test.
+            ===============
+          MESSAGE
+
           # Test if command needs to be executed in zombie environment
           #
           # @return [Bool]
@@ -28,10 +42,19 @@ def zombie?
           def action
             soft_fail(License.call(world))
               .bind { bootstrap }
+              .bind(&method(:validate_tests))
               .bind(&Runner.public_method(:call))
               .bind(&method(:from_result))
           end
 
+          def validate_tests(environment)
+            if environment.integration.all_tests.length.zero?
+              Either::Left.new(NO_TESTS_MESSAGE)
+            else
+              Either::Right.new(environment)
+            end
+          end
+
           def from_result(result)
             if result.success?
               Either::Right.new(nil)

lib/mutant/reporter/cli/printer/mutation.rb

@@ -8,7 +8,7 @@ class Printer
         class Mutation < self
           NO_DIFF_MESSAGE = <<~'MESSAGE'
             --- Internal failure ---
-            BUG: A generted mutation did not result in exactly one diff hunk!
+            BUG: A generated mutation did not result in exactly one diff hunk!
             This is an invariant violation by the mutation generation engine.
             Please report a reproduction to https://github.com/mbj/mutant
             Original unparsed source:

lib/mutant/reporter/cli/printer/mutation_result.rb

@@ -27,7 +27,7 @@ class MutationResult < self
 
           NO_DIFF_MESSAGE = <<~'MESSAGE'
             --- Internal failure ---
-            BUG: A generted mutation did not result in exactly one diff hunk!
+            BUG: A generated mutation did not result in exactly one diff hunk!
             This is an invariant violation by the mutation generation engine.
             Please report a reproduction to https://github.com/mbj/mutant
             Original unparsed source:

spec/unit/mutant/cli_spec.rb

@@ -679,10 +679,10 @@ def self.main_body
           [
             license_validation_event,
             [:stderr, :puts, 'license-error'],
-            [:stderr, :puts, "[Mutant-License-Error]: Soft fail, continuing in 40 seconds\n"],
+            [:stderr, :puts, "[Mutant-License-Error]: Soft fail, continuing in 60 seconds\n"],
             [:stderr, :puts, "[Mutant-License-Error]: Next major version will enforce the license\n"],
             [:stderr, :puts, "[Mutant-License-Error]: See https://github.com/mbj/mutant#licensing\n"],
-            [:sleep, 40],
+            [:sleep, 60],
             [
               :load_config_file,
               world
@@ -748,28 +748,49 @@ def self.main_body
         end
 
         context 'on runner success with unsuccessful result' do
-          let(:expected_exit) { false             }
-          let(:runner_result) { right(env_result) }
+          context 'on alive mutations' do
+            let(:expected_exit) { false             }
+            let(:runner_result) { right(env_result) }
+
+            let(:env_result) do
+              instance_double(
+                Mutant::Result::Env,
+                success?: false
+              )
+            end
 
-          let(:env_result) do
-            instance_double(
-              Mutant::Result::Env,
-              success?: false
-            )
+            let(:expected_events) do
+              [
+                *super(),
+                [
+                  :stderr,
+                  :puts,
+                  'Uncovered mutations detected, exiting nonzero!'
+                ]
+              ]
+            end
+
+            include_examples 'CLI run'
           end
 
-          let(:expected_events) do
-            [
-              *super(),
+          context 'on not having found tests' do
+            let(:tests) { [] }
+
+            let(:expected_events) do
               [
-                :stderr,
-                :puts,
-                'Uncovered mutations detected, exiting nonzero!'
+                *super()[0..-2],
+                [
+                  :stderr,
+                  :puts,
+                  Mutant::CLI::Command::Environment::Run::NO_TESTS_MESSAGE
+                ]
               ]
-            ]
-          end
+            end
 
-          include_examples 'CLI run'
+            let(:expected_exit) { false }
+
+            include_examples 'CLI run'
+          end
         end
 
         context 'with valid subject expression' do

spec/unit/mutant/reporter/cli/printer/mutation_result_spec.rb

@@ -64,7 +64,7 @@
             -----------------------
             Killfork: #<InstanceDouble(Process::Status) (anonymous)>
             --- Internal failure ---
-            BUG: A generted mutation did not result in exactly one diff hunk!
+            BUG: A generated mutation did not result in exactly one diff hunk!
             This is an invariant violation by the mutation generation engine.
             Please report a reproduction to https://github.com/mbj/mutant
             Original unparsed source: